Update ax_cc_maxopt m4 macro (#617)

Keeps libffi's specific changes
(https://github.com/libffi/libffi/commit/cec3a3a201f17a7f018f25e1a0917bd5206e5a5a#diff-2396a1256ac4b1c6849c931ddb8018bdd984bb2383be21bb819a33b95d8d603f)
and updates to the latest ax_cc_maxopt.m4
(http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=commit;h=73ee1b396c21062ee8eeb8721ba5323322110fb5):

ax_cc_maxopt.m4: retain setting of CFLAGS by configure

AX_CC_MAXOPT checks whether CFLAGS was set by the user; if so, the user’s
setting is respected. This behavior is retained, of course.

However, AX_CC_MAXOPT was then setting CFLAGS="". This overrode the default
setting by configure, which usually includes -g. Hence, if CFLAGS was not
set by the user, retain the default setting, to preserve the ability to
debug.

A typical default setting from configure is "-g -O2". This means that
AX_CC_MAXOPT might typically set CFLAGS to "-g -O2 -O3". This is fine,
because the later -O3 will override the earlier -O2. (The only assumption is
that all compilers that AX_CC_MAXOPT knows behave in this sane way.)

diff --git a/m4/ax_cc_maxopt.m4 b/m4/ax_cc_maxopt.m4
index 9e7f1ee4a1dd1fbd7d1537dad3ba3e350aa75c2d..027b6d8279cc37402f40dfe019447abbdaa5106d 100644 (file)
--- a/m4/ax_cc_maxopt.m4
+++ b/m4/ax_cc_maxopt.m4
@@ -55,7 +55,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 17
+#serial 18
 
 AC_DEFUN([AX_CC_MAXOPT],
 [
@@ -68,19 +68,18 @@ AC_ARG_ENABLE(portable-binary, [AS_HELP_STRING([--enable-portable-binary], [disa
 
 # Try to determine "good" native compiler flags if none specified via CFLAGS
 if test "$ac_test_CFLAGS" != "set"; then
-  CFLAGS=""
   case $ax_cv_c_compiler_vendor in
-    dec) CFLAGS="-newc -w0 -O5 -ansi_alias -ansi_args -fp_reorder -tune host"
+    dec) CFLAGS="$CFLAGS -newc -w0 -O5 -ansi_alias -ansi_args -fp_reorder -tune host"
         if test "x$acx_maxopt_portable" = xno; then
            CFLAGS="$CFLAGS -arch host"
          fi;;
 
-    sun) CFLAGS="-native -fast -xO5 -dalign"
+    sun) CFLAGS="$CFLAGS -native -fast -xO5 -dalign"
         if test "x$acx_maxopt_portable" = xyes; then
           CFLAGS="$CFLAGS -xarch=generic"
          fi;;
 
-    hp)  CFLAGS="+Oall +Optrs_ansi +DSnative"
+    hp)  CFLAGS="$CFLAGS +Oall +Optrs_ansi +DSnative"
         if test "x$acx_maxopt_portable" = xyes; then
           CFLAGS="$CFLAGS +DAportable"
         fi;;
@@ -91,8 +90,8 @@ if test "$ac_test_CFLAGS" != "set"; then
            xlc_opt="-qtune=auto"
         fi
          AX_CHECK_COMPILE_FLAG($xlc_opt,
-               CFLAGS="-O3 -qansialias -w $xlc_opt",
-               [CFLAGS="-O3 -qansialias -w"
+               CFLAGS="$CFLAGS -O3 -qansialias -w $xlc_opt",
+               [CFLAGS="$CFLAGS -O3 -qansialias -w"
                 echo "******************************************************"
                 echo "*  You seem to have the IBM  C compiler.  It is      *"
                 echo "*  recommended for best performance that you use:    *"
@@ -105,7 +104,7 @@ if test "$ac_test_CFLAGS" != "set"; then
                 echo "******************************************************"])
          ;;
 
-    intel) CFLAGS="-O3 -ansi_alias"
+    intel) CFLAGS="$CFLAGS -O3 -ansi_alias"
        if test "x$acx_maxopt_portable" = xno; then
          icc_archflag=unknown
          icc_flags=""
@@ -146,7 +145,7 @@ if test "$ac_test_CFLAGS" != "set"; then
 
     gnu)
      # default optimization flags for gcc on all systems
-     CFLAGS="-O3 -fomit-frame-pointer"
+     CFLAGS="$CFLAGS -O3 -fomit-frame-pointer"
 
      # -malign-double for x86 systems
      # libffi local change -- don't align double, as it changes the ABI
@@ -164,7 +163,7 @@ if test "$ac_test_CFLAGS" != "set"; then
 
     microsoft)
      # default optimization flags for MSVC opt builds
-     CFLAGS="-O2"
+     CFLAGS="$CFLAGS -O2"
      ;;
   esac
 
@@ -176,7 +175,7 @@ if test "$ac_test_CFLAGS" != "set"; then
        echo "* (otherwise, a default of CFLAGS=-O3 will be used)    *"
        echo "********************************************************"
        echo ""
-        CFLAGS="-O3"
+        CFLAGS="$CFLAGS -O3"
   fi
 
   AX_CHECK_COMPILE_FLAG($CFLAGS, [], [
@@ -187,7 +186,6 @@ if test "$ac_test_CFLAGS" != "set"; then
         echo "* Use ./configure CFLAGS=... to specify your own flags *"
         echo "********************************************************"
         echo ""
-        CFLAGS=""
   ])
 
 fi