Add configure check for -Wframe-larger-than=<size>

It turns out the gcc option -Wframe-larger-than=<size> which I recently
added to the build system is not supported in older versions of gcc.
Since this is just a flag to ensure I keep stack usage under control
I've added a configure check to detect if gcc supports it.  If it's
available we use it in the proper places, if it's not we don't.

cmd/ztest/Makefile.am

@@ -1,6 +1,6 @@
 include $(top_srcdir)/config/Rules.am
 
-AM_CFLAGS += -Wframe-larger-than=1024
+AM_CFLAGS += $(FRAME_LARGER_THAN)
 
 DEFAULT_INCLUDES += \
 	-I${top_srcdir}/lib/libspl/include \

config/user-frame-larger-than.m4

@@ -0,0 +1,22 @@
+dnl #
+dnl # Check if gcc supports -Wframe-larger-than=<size> option.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_USER_FRAME_LARGER_THAN], [
+	AC_MSG_CHECKING([for -Wframe-larger-than=<size> support])
+
+	saved_flags="$CFLAGS"
+	CFLAGS="$CFLAGS -Wframe-larger-than=1024"
+
+	AC_RUN_IFELSE(AC_LANG_PROGRAM( [], []),
+	[
+		FRAME_LARGER_THAN=-Wframe-larger-than=1024
+		AC_MSG_RESULT([yes])
+	],
+	[
+		FRAME_LARGER_THAN=
+		AC_MSG_RESULT([no])
+	])
+
+	CFLAGS="$saved_flags"
+        AC_SUBST([FRAME_LARGER_THAN])
+])

config/user.m4

@@ -8,4 +8,5 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_ZLIB
 	ZFS_AC_CONFIG_USER_LIBUUID
 	ZFS_AC_CONFIG_USER_LIBBLKID
+	ZFS_AC_CONFIG_USER_FRAME_LARGER_THAN
 ])

lib/libzpool/Makefile.am

@@ -1,6 +1,6 @@
 include $(top_srcdir)/config/Rules.am
 
-AM_CFLAGS += -Wframe-larger-than=1024
+AM_CFLAGS += $(FRAME_LARGER_THAN)
 
 SUBDIRS = include
 DEFAULT_INCLUDES += \