From: Daniel Drake <dsd@gentoo.org>

gamin ignores user-supplied CFLAGS.
http://bugzilla.gnome.org/show_bug.cgi?id=450262
https://bugs.gentoo.org/show_bug.cgi?id=178266

Index: configure.in
===================================================================
--- configure.in	(revision 325)
+++ configure.in	(working copy)
@@ -1,13 +1,12 @@
 dnl Process this file with autoconf to produce a configure script.
-
-# get any external flags setting before we start playing with the CFLAGS variable
-ENV_CFLAGS=$CFLAGS
-
 AC_PREREQ(2.52)
 AC_INIT(libgamin)
 AM_CONFIG_HEADER(config.h)
 AC_CANONICAL_SYSTEM
 
+# get any external flags setting before we start playing with the CFLAGS variable
+ENV_CFLAGS="$CFLAGS"
+
 GAMIN_MAJOR_VERSION=0
 GAMIN_MINOR_VERSION=1
 GAMIN_MICRO_VERSION=9
@@ -37,6 +36,12 @@
 AC_PROG_INSTALL
 AC_PROG_MAKE_SET
 
+dnl If the user set no CFLAGS, then don't assume the autotools defaults of
+dnl "-g -O2". We set default CFLAGS later based on the --disable-debug flag.
+if test -z "$ENV_CFLAGS"; then
+	CFLAGS=""
+fi
+
 dnl for the spec file
 RELDATE=`date +'%a %b %e %Y'`
 AC_SUBST(RELDATE)
@@ -506,44 +511,45 @@
 AC_MSG_CHECKING(for more compiler warnings)
 if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
 	AC_MSG_RESULT(yes)
-	CFLAGS="\
+	warning_cflags="\
  -Wall\
  -Wchar-subscripts -Wmissing-declarations -Wmissing-prototypes\
  -Wnested-externs\
  -Wsign-compare"
 
+	SAVE_CFLAGS="$CFLAGS"
 	for option in -Wno-sign-compare; do
-		SAVE_CFLAGS="$CFLAGS"
-		CFLAGS="$CFLAGS $option"
+		CFLAGS="$option"
 		AC_MSG_CHECKING([whether gcc understands $option])
 		AC_TRY_COMPILE([], [],
 			has_option=yes,
 			has_option=no,)
-		if test $has_option = no; then
-			CFLAGS="$SAVE_CFLAGS"
+		if test "$has_option" != "no"; then
+			warning_cflags="$warning_cflags $option"
 		fi
 		AC_MSG_RESULT($has_option)
 		unset has_option
-		unset SAVE_CFLAGS
 	done
+	CFLAGS="$SAVE_CFLAGS"
 	unset option
 else
 	AC_MSG_RESULT(no)
-	unset CFLAGS
 fi
 
 if test "$GCC" = "yes"; then
 	if test "$debug" = "yes"; then
-		CFLAGS="$CFLAGS -g"
+		debug_cflags="-g"
 	else
-		#don't optimise with -g
+		# autotools defaults to "-O2 -g" for cflags, but we don't
+		# want -g in non-debug builds
 		if test -z "$ENV_CFLAGS"; then
-			ENV_CFLAGS="-O2"
+			CFLAGS="-O2"
 		fi
 	fi
 fi
 
-CFLAGS="$CFLAGS $ENV_CFLAGS"
+AM_CFLAGS="$warning_cflags $debug_cflags"
+AC_SUBST(AM_CFLAGS)
 
 dnl ==========================================================================
 
@@ -569,7 +575,7 @@
         prefix:                   ${prefix}
         source code location:     ${srcdir}
         compiler:                 ${CC}
-        compiler flags:           ${CFLAGS}
+        compiler flags:           ${AM_CFLAGS} ${CFLAGS}
                                                                                 
 	backends:                 ${backends}
 	build documentation:      ${build_docs}