Bug 1379835 - Don't filter out -idirafter flag when building elfhack injected code. r=gps

--HG--
extra : rebase_source : 4c6eea5ec9c592873ef94cb0c674fc4b26ef385c

build/unix/elfhack/inject/Makefile.in

@@ -10,4 +10,4 @@ $(CSRCS): %.c: ../inject.c
 
 GARBAGE += $(CSRCS)
 
-CFLAGS := -O2 -fno-stack-protector $(filter -m% -I%,$(CFLAGS))
+CFLAGS := -O2 -fno-stack-protector $(filter -m% -I% -idirafter%,$(subst -idirafter ,-idirafter,$(CFLAGS)))