Better check for compiler flag capability

When adding a `-Wno-some-error` flag, instead of trying to check for
`-Wno-some-error` support this checks for `-Wsome-error` support.
This is done because currently there's the a problem when compiling
citus with `./configure CFLAGS=-Werror`. If there's a warning (which is
then converted to an error) in addition to this error, the output will contain
the following message with GCC 7:

```
cc1: error: unrecognized command line option ‘-Wno-gnu-variable-sized-type-not-at-end’ [-Werror]
```

This is because of the following behaviour of GCC in case of unknown warnings:

> When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC
> emits a diagnostic stating that the option is not recognized.  However, if the
> -Wno- form is used, the behavior is slightly different: no diagnostic is
> produced for -Wno-unknown-warning unless other diagnostics are being produced.
> This allows the use of new -Wno- options with old compilers, but if something
> goes wrong, the compiler warns that an unrecognized option is present.

By changing the check to `-Wsome-error`, the check will actually fail
when the warning is not supported. Instead of silently being ignored
when checking, but then coming up when another error happens.

configure

@@ -3639,7 +3639,11 @@ if ${citusac_cv_prog_cc_cflags__std_gnu99+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -std=gnu99"
+flag=-std=gnu99
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3674,7 +3678,11 @@ if ${citusac_cv_prog_cc_cflags__Wall+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wall"
+flag=-Wall
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3709,7 +3717,11 @@ if ${citusac_cv_prog_cc_cflags__Wextra+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wextra"
+flag=-Wextra
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3745,7 +3757,11 @@ if ${citusac_cv_prog_cc_cflags__Wno_unused_parameter+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wno-unused-parameter"
+flag=-Wno-unused-parameter
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3780,7 +3796,11 @@ if ${citusac_cv_prog_cc_cflags__Wno_sign_compare+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wno-sign-compare"
+flag=-Wno-sign-compare
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3815,7 +3835,11 @@ if ${citusac_cv_prog_cc_cflags__Wno_missing_field_initializers+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wno-missing-field-initializers"
+flag=-Wno-missing-field-initializers
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3850,7 +3874,11 @@ if ${citusac_cv_prog_cc_cflags__Wno_clobbered+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wno-clobbered"
+flag=-Wno-clobbered
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3885,7 +3913,11 @@ if ${citusac_cv_prog_cc_cflags__Wno_gnu_variable_sized_type_not_at_end+:} false;
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wno-gnu-variable-sized-type-not-at-end"
+flag=-Wno-gnu-variable-sized-type-not-at-end
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3921,7 +3953,11 @@ if ${citusac_cv_prog_cc_cflags__Wendif_labels+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wendif-labels"
+flag=-Wendif-labels
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3956,7 +3992,11 @@ if ${citusac_cv_prog_cc_cflags__Wmissing_format_attribute+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wmissing-format-attribute"
+flag=-Wmissing-format-attribute
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -3991,7 +4031,11 @@ if ${citusac_cv_prog_cc_cflags__Wmissing_declarations+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wmissing-declarations"
+flag=-Wmissing-declarations
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -4026,7 +4070,11 @@ if ${citusac_cv_prog_cc_cflags__Wmissing_prototypes+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wmissing-prototypes"
+flag=-Wmissing-prototypes
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -4061,7 +4109,11 @@ if ${citusac_cv_prog_cc_cflags__Wshadow+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Wshadow"
+flag=-Wshadow
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -4096,7 +4148,11 @@ if ${citusac_cv_prog_cc_cflags__Werror_vla+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS -Werror=vla"
+flag=-Werror=vla
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext

configure.in

@@ -136,7 +136,11 @@ AC_DEFUN([CITUSAC_PROG_CC_CFLAGS_OPT],
 [define([Ac_cachevar], [AS_TR_SH([citusac_cv_prog_cc_cflags_$1])])dnl
 AC_CACHE_CHECK([whether $CC supports $1], [Ac_cachevar],
 [citusac_save_CFLAGS=$CFLAGS
-CFLAGS="$citusac_save_CFLAGS $1"
+flag=$1
+case $flag in -Wno*)
+	 flag=-W$(echo $flag | cut -c 6-)
+esac
+CFLAGS="$citusac_save_CFLAGS $flag"
 ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 _AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],