Disable -Wsometimes-uninitialized warnings in the 9.2 branch.

In 9.2, we didn't yet teach the compiler that elog(ERROR) doesn't
return, which means that the compiler's opinion about whether
variable dereferences are reachable isn't worth much.  Back-patching
the commits that fixed that seems unduly invasive, so instead silence
related complaints with a big hammer.

-Wsometimes-uninitialized is a clang-ism; gcc seems to spell
this warning option differently.  However, I do not observe
any such compiler warnings in 9.2 with gcc 11.2.1, so for now
we needn't do anything for gcc.

Discussion: https://postgr.es/m/d0316012-ece7-7b7e-2d36-9c38cb77cb3b@enterprisedb.com

configure

@@ -4670,6 +4670,73 @@ fi
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-stringop-truncation"
   fi
+  # Similarly disable sometimes-uninitialized warnings, because in this
+  # branch we have not taught the compiler that elog(ERROR) doesn't return,
+  # so that the compiler's opinion about this isn't worth much.
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:$LINENO: checking whether $CC supports -Wsometimes-uninitialized" >&5
+$as_echo_n "checking whether $CC supports -Wsometimes-uninitialized... " >&6; }
+if test "${pgac_cv_prog_cc_cflags__Wsometimes_uninitialized+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -Wsometimes-uninitialized"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_prog_cc_cflags__Wsometimes_uninitialized=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_prog_cc_cflags__Wsometimes_uninitialized=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_prog_cc_cflags__Wsometimes_uninitialized" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__Wsometimes_uninitialized" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__Wsometimes_uninitialized" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wsometimes-uninitialized"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-sometimes-uninitialized"
+  fi
 elif test "$ICC" = yes; then
   # Intel's compiler has a bug/misoptimization in checking for
   # division by NAN (NaN == 0), -mp1 fixes it, so add it to the CFLAGS.

configure.in

@@ -453,6 +453,14 @@ if test "$GCC" = yes -a "$ICC" = no; then
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-stringop-truncation"
   fi
+  # Similarly disable sometimes-uninitialized warnings, because in this
+  # branch we have not taught the compiler that elog(ERROR) doesn't return,
+  # so that the compiler's opinion about this isn't worth much.
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wsometimes-uninitialized])
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-sometimes-uninitialized"
+  fi
 elif test "$ICC" = yes; then
   # Intel's compiler has a bug/misoptimization in checking for
   # division by NAN (NaN == 0), -mp1 fixes it, so add it to the CFLAGS.