x86_64: libm fixes

* Makefile update for x86_64 target
* amd64 arch files

Change-Id: I8f17e3338bffd89a3086fbddd1e91bb4619eac1b
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
diff --git a/libm/Android.mk b/libm/Android.mk
index 0d2c843..3e769e7 100644
--- a/libm/Android.mk
+++ b/libm/Android.mk
@@ -226,6 +226,9 @@
 libm_x86_includes := $(LOCAL_PATH)/i386 $(LOCAL_PATH)/i387
 libm_x86_src_files := i387/fenv.c
 
+libm_x86_64_includes := $(LOCAL_PATH)/amd64 $(LOCAL_PATH)/i387
+libm_x86_64_src_files := amd64/fenv.c
+
 libm_mips_cflags := -fno-builtin-rintf -fno-builtin-rint
 libm_mips_includes := $(LOCAL_PATH)/mips
 libm_mips_src_files := mips/fenv.c