enable build of graphics/libraw on gcc4 arches

Hi!
This patch enables build of libraw on other gcc4 arches, not only arm.
Tested on macppc.
OK?

Index: Makefile
===================================================================
RCS file: /cvs/ports/graphics/libraw/Makefile,v
retrieving revision 1.29
diff -u -r1.29 Makefile
--- Makefile 16 Nov 2017 23:20:39 -0000 1.29
+++ Makefile 3 Dec 2017 07:51:00 -0000
@@ -23,8 +23,6 @@
MASTER_SITES = https://www.libraw.org/data/

COMPILER = base-clang ports-gcc
-# for atomic builtins (__sync_fetch_and_add_4)
-MODGCC4_ARCHS = arm

LIB_DEPENDS = graphics/jasper \
graphics/lcms2