[PATCH 1/2] Add CC_CHECK_LDFLAGS_APPEND m4 macro.

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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.
---
 m4/attributes.m4 |   41 ++++++++++++++++++++++++++++++++++++-----
 1 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/m4/attributes.m4 b/m4/attributes.m4
index 9d561c2..cc88fb3 100644
--- a/m4/attributes.m4
+++ b/m4/attributes.m4
@@ -81,12 +81,11 @@ 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; }],
@@ -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], [
-- 
1.7.4.1
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