Compile safestringlib using regular configure

This is needed to automatically generate .bc (bitcode) files when
postgres is compiled with llvmjit support.

It also has the advantage that cmake is not required for the build
anymore.

src/backend/distributed/Makefile

@@ -7,13 +7,6 @@ safestringlib_builddir = $(citus_top_builddir)/vendor/safestringlib/build
 safestringlib_a = $(safestringlib_builddir)/libsafestring_static.a
 safestringlib_sources = $(wildcard $(safestringlib_srcdir)/safeclib/*)
 
-# Use cmake3 if it exists, otherwise just use the string "cmake" and let bash
-# figure out its exact path later.
-# Using "which cmake" instead will make the error very hard to understand if
-# you have neither "cmake3" or "cmake" in path. In that case the "CMAKE3"
-# variable would be an empty string.
-CMAKE3 = $(shell which cmake3 || echo cmake)
-
 MODULE_big = citus
 EXTENSION = citus
 
@@ -23,7 +16,11 @@ generated_sql_files = $(patsubst %,$(citus_abs_srcdir)/build/%,$(template_sql_fi
 DATA_built = $(generated_sql_files)
 
 # directories with source files
-SUBDIRS = . commands connection ddl deparser executor master metadata planner progress relay test transaction utils worker
+SUBDIRS = . commands connection ddl deparser executor master metadata planner progress relay safeclib test transaction utils worker
+
+# Symlinks are not copied over to the build directory if a separete build
+# directory is used during configure (such as on CI)
+ENSURE_SUBDIRS_EXIST := $(shell mkdir -p $(SUBDIRS))
 
 # That patsubst rule searches all directories listed in SUBDIRS for .c
 # files, and adds the corresponding .o files to OBJS
@@ -50,23 +47,11 @@ utils/citus_version.o: $(CITUS_VERSION_INVALIDATE)
 
 SHLIB_LINK += $(filter -lssl -lcrypto -lssleay32 -leay32, $(LIBS))
 
-override LDFLAGS += $(safestringlib_a)
 override CPPFLAGS += -I$(libpq_srcdir) -I$(safestringlib_srcdir)/include
 
 SQL_DEPDIR=.deps/sql
 SQL_BUILDDIR=build/sql
 
-$(safestringlib_a): $(safestringlib_sources)
-	rm -rf $(safestringlib_builddir)
-	mkdir -p $(safestringlib_builddir)
-	@# exports of LDFLAGS and CPPFLAGS are to make sure the ones from this
-	@# Makefile are not used
-	+cd $(safestringlib_builddir) && \
-		export LDFLAGS='' && export CPPFLAGS='' && \
-		$(CMAKE3) $(safestringlib_srcdir) && make
-
-citus.so: $(safestringlib_a)
-
 $(generated_sql_files): $(citus_abs_srcdir)/build/%: %
 	@mkdir -p $(citus_abs_srcdir)/$(SQL_DEPDIR) $(citus_abs_srcdir)/$(SQL_BUILDDIR)
 	cd $(citus_abs_srcdir) && cpp -undef -w -P -MMD -MP -MF$(SQL_DEPDIR)/$(*F).Po -MT$@ $< > $@

src/backend/distributed/safeclib

@@ -0,0 +1 @@
+../../../vendor/safestringlib/safeclib/