build: add _ASMLANGUAGE to all asm files

This avoids asm files from having to explicitly define the _ASMLANGUAGE
symbol themselves.

Change-Id: I71f5a169f75d7443a58a0365a41c55b20dae3029
Signed-off-by: Benjamin Walsh <walsh.benj@gmail.com>
diff --git a/Makefile b/Makefile
index 71ad2c8..627d11a 100644
--- a/Makefile
+++ b/Makefile
@@ -399,7 +399,7 @@
 		-ffunction-sections -fdata-sections \
 		-fno-rtti -fno-exceptions
 
-KBUILD_AFLAGS   := -c -g -xassembler-with-cpp
+KBUILD_AFLAGS   := -c -g -xassembler-with-cpp -D_ASMLANGUAGE
 
 LDFLAGS += $(call ld-option,-nostartfiles)
 LDFLAGS += $(call ld-option,-nodefaultlibs)