--- configure.orig	Wed Aug  9 18:17:28 2006
+++ configure.in	Wed Aug  9 18:23:42 2006
@@ -531,22 +531,40 @@
 AC_CHECK_HEADERS([stdint.h inttypes.h sys/int_types.h])
 AC_CHECK_TYPES([uint64_t, uint128_t])
 
-dnl Use lots of warning flags with GCC
+AC_DEFUN([AC_CC_TRY_FLAG], [
+  AC_MSG_CHECKING([whether $CC supports $1])
 
-WARN_CFLAGS=""
+  ac_save_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS $1"
+
+  AC_COMPILE_IFELSE([ ], [ac_cc_flag=yes], [ac_cc_flag=no])
+  CFLAGS="$ac_save_CFLAGS"
+
+  if test "x$ac_cc_flag" = "xyes"; then
+    ifelse([$2], , :, [$2])
+  else
+    ifelse([$3], , :, [$3])
+  fi
+  AC_MSG_RESULT([$ac_cc_flag])
+])
 
-dnl XXX: Here are some warnings we'd like to eanble, but it looks like
-dnl we'll need to make them conditional on gcc version >= 4 or so:
-dnl
-dnl -Wstrict-aliasing=2 -Winit-self -Wunsafe-loop-optimizations
-dnl -Wdeclaration-after-statement -Wold-style-definition
+dnl Use lots of warning flags with GCC
+WARN_CFLAGS=""
 
 if test "x$GCC" = "xyes"; then
+	# some warnings are not supported by all versions of gcc
+	MAYBE_WARN="-Wpacked -Wswitch-enum -Wmissing-format-attribute \
+	-Wstrict-aliasing=2 -Winit-self -Wunsafe-loop-optimizations \
+	-Wdeclaration-after-statement -Wold-style-definition"
+
 	WARN_CFLAGS="-Wall -Wsign-compare -Werror-implicit-function-declaration \
-	-Wpointer-arith -Wwrite-strings -Wswitch-enum \
-	-Wpacked -Wmissing-format-attribute -Wstrict-prototypes \
+	-Wpointer-arith -Wwrite-strings -Wstrict-prototypes \
 	-Wmissing-prototypes -Wmissing-declarations \
 	-Wnested-externs -fno-strict-aliasing"
+
+	for W in $MAYBE_WARN; do
+		AC_CC_TRY_FLAG([$W], [WARN_CFLAGS="$WARN_CFLAGS $W"])
+	done
 fi
 
 AC_SUBST(WARN_CFLAGS)