sh: Fix SH4 build with GCC versions without -m4-nofpu

Pass -m4 instead of -m4-nofpu to GCC versions which do not support
the -m4-nofpu option.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/arch/sh/cpu/sh4/config.mk b/arch/sh/cpu/sh4/config.mk
index d62d285..23fec66 100644
--- a/arch/sh/cpu/sh4/config.mk
+++ b/arch/sh/cpu/sh4/config.mk
@@ -6,4 +6,4 @@
 # (C) Copyright 2007
 # Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
 #
-PLATFORM_CPPFLAGS += -m4-nofpu
+PLATFORM_CPPFLAGS += $(call cc-option,-m4-nofpu,-m4)