configure: Use -Wno-maybe-uninitialized iff compiler supports it

clang does not support the flag.

configure

@@ -7557,6 +7557,32 @@ config_vars="$config_vars
 config-cflags-wno-ignored-attributes = $libc_cv_wno_ignored_attributes"
 
 
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for -Wno-maybe-uninitialized" >&5
+printf %s "checking for -Wno-maybe-uninitialized... " >&6; }
+if test ${libc_cv_wno_maybe_uninitialized+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e) 		if { ac_try='${CC-cc} -Werror -Wno-maybe-uninitialized -xc /dev/null -S -o /dev/null'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+then :
+  libc_cv_wno_maybe_uninitialized=-Wno-maybe-uninitialized
+else case e in #(
+  e) libc_cv_wno_maybe_uninitialized= ;;
+esac
+fi
+ ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_wno_maybe_uninitialized" >&5
+printf "%s\n" "$libc_cv_wno_maybe_uninitialized" >&6; }
+config_vars="$config_vars
+config-cflags-wno-maybe-uninitialized = $libc_cv_wno_maybe_uninitialized"
+
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether cc puts quotes around section names" >&5
 printf %s "checking whether cc puts quotes around section names... " >&6; }
 if test ${libc_cv_have_section_quotes+y}

configure.ac

@@ -1425,6 +1425,15 @@ LIBC_CONFIG_VAR([config-cflags-wno-ignored-attributes],
 		[$libc_cv_wno_ignored_attributes])
 AC_SUBST(libc_cv_test_wno_ignored_attributes)
 
+AC_CACHE_CHECK([for -Wno-maybe-uninitialized],
+                libc_cv_wno_maybe_uninitialized, [dnl
+		LIBC_TRY_CC_OPTION([-Werror -Wno-maybe-uninitialized],
+				   [libc_cv_wno_maybe_uninitialized=-Wno-maybe-uninitialized],
+				   [libc_cv_wno_maybe_uninitialized=])
+])
+LIBC_CONFIG_VAR([config-cflags-wno-maybe-uninitialized],
+		[$libc_cv_wno_maybe_uninitialized])
+
 AC_CACHE_CHECK(whether cc puts quotes around section names,
 	       libc_cv_have_section_quotes,
 	       [cat > conftest.c <<EOF

timezone/Makefile

@@ -68,7 +68,7 @@ tz-cflags = -DTZDIR='"$(zonedir)"' \
 	    -DTZDEFRULES='"$(posixrules-file)"' \
 	    -DTM_GMTOFF=tm_gmtoff -DTM_ZONE=tm_zone \
 	    -DHAVE_GETTEXT -DUSE_LTZ=0 -D_ISOMAC -DTZ_DOMAIN='"libc"' \
-	    -include $(common-objpfx)config.h -Wno-maybe-uninitialized
+	    -include $(common-objpfx)config.h $(config-cflags-wno-maybe-uninitialized)
 
 # The -Wno-unused-variable flag is used to prevent GCC 6
 # from warning about time_t_min and time_t_max which are