Revert "toolchain: drop $(REVISION) from GCC version"

This reverts commit 9292f32fd9.

Downstream patches may change the output. If the GCC version doesn't
incooperate the patches somehow (hash, git commit, ...), ccache may not
invalidate existing cache.

Revert this until a cleaner solution is found.

Signed-off-by: Paul Spooren <mail@aparcar.org>

toolchain/gcc/common.mk

@@ -45,7 +45,7 @@ endif
 PATCH_DIR=../patches-$(GCC_MAJOR_VERSION).x
 
 BUGURL=http://bugs.openwrt.org/
-PKGVERSION=OpenWrt GCC $(PKG_VERSION)
+PKGVERSION=OpenWrt GCC $(PKG_VERSION) $(REVISION)
 
 HOST_BUILD_PARALLEL:=1