Add CC_CHECK_LDFLAGS_APPEND m4 macro.

This is mostly just preparation for the next patch. But this macro is
used for flags that are only needed during linking but that don't
make sense for normal compilation.

I saw this exact type of patch online for systemd, but it never seems to
have actually been incorporated into their attributes.m4.

diff --git a/m4/attributes.m4 b/m4/attributes.m4
index 9d561c244bf81ac321774905132ab61e01b4730a..20d05e4bde8869db5022da1b1bebe9480dd03dbb 100644 (file)
--- a/m4/attributes.m4
+++ b/m4/attributes.m4
@@ -81,15 +81,14 @@ AC_DEFUN([CC_CHECK_CFLAGS_APPEND], [
   done
 ])
 
-dnl Check if the flag is supported by linker (cacheable)
-dnl CC_CHECK_LDFLAGS([FLAG], [ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
+dnl Check if the flag is supported by linker
+dnl CC_CHECK_LDFLAGS_SILENT([FLAG], [ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
 
-AC_DEFUN([CC_CHECK_LDFLAGS], [
-  AC_CACHE_CHECK([if $CC supports $1 flag],
-    AS_TR_SH([cc_cv_ldflags_$1]),
+AC_DEFUN([CC_CHECK_LDFLAGS_SILENT], [
+  AC_CACHE_VAL(AS_TR_SH([cc_cv_ldflags_$1]),
     [ac_save_LDFLAGS="$LDFLAGS"
      LDFLAGS="$LDFLAGS $1"
-     AC_LINK_IFELSE([int main() { return 1; }],
+     AC_LINK_IFELSE([AC_LANG_SOURCE([int main() { return 1; }])],
        [eval "AS_TR_SH([cc_cv_ldflags_$1])='yes'"],
        [eval "AS_TR_SH([cc_cv_ldflags_$1])="])
      LDFLAGS="$ac_save_LDFLAGS"
@@ -99,6 +98,38 @@ AC_DEFUN([CC_CHECK_LDFLAGS], [
     [$2], [$3])
 ])
 
+dnl Check if the flag is supported by linker (cacheable)
+dnl CC_CHECK_LDFLAGS([FLAG], [ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
+
+AC_DEFUN([CC_CHECK_LDFLAGS], [
+  AC_CACHE_CHECK([if $CC supports $1 flag],
+    AS_TR_SH([cc_cv_ldflags_$1]),
+    CC_CHECK_LDFLAGS_SILENT([$1]) dnl Don't execute actions here!
+  )
+
+  AS_IF([eval test x$]AS_TR_SH([cc_cv_ldflags_$1])[ = xyes],
+    [$2], [$3])
+])
+
+dnl CC_CHECK_LDFLAG_APPEND(FLAG, [action-if-found], [action-if-not-found])
+dnl Check for LDFLAG and appends them to LDFLAGS if supported
+AC_DEFUN([CC_CHECK_LDFLAG_APPEND], [
+  AC_CACHE_CHECK([if $CC supports $1 flag],
+    AS_TR_SH([cc_cv_ldflags_$1]),
+    CC_CHECK_LDFLAGS_SILENT([$1]) dnl Don't execute actions here!
+  )
+
+  AS_IF([eval test x$]AS_TR_SH([cc_cv_ldflags_$1])[ = xyes],
+    [LDFLAGS="$LDFLAGS $1"; DEBUG_LDFLAGS="$DEBUG_LDFLAGS $1"; $2], [$3])
+])
+
+dnl CC_CHECK_LDFLAGS_APPEND([FLAG1 FLAG2], [action-if-found], [action-if-not])
+AC_DEFUN([CC_CHECK_LDFLAGS_APPEND], [
+  for flag in $1; do
+    CC_CHECK_LDFLAG_APPEND($flag, [$2], [$3])
+  done
+])
+
 dnl define the LDFLAGS_NOUNDEFINED variable with the correct value for
 dnl the current linker to avoid undefined references in a shared object.
 AC_DEFUN([CC_NOUNDEFINED], [