Cleanup x86 and x86_64 flags

-mandroid, -D__ANDROID__ is on by the toolchain;
-msse3 moved to llvm_config, it seems it's required only there;
__cxa_atexit is provided by libc now;
USE_SSE2 should not be used anywhere, it's always true;
remove -mstackreallign and -mfpmath=sse as useless for x86_64;

Change-Id: Ib7739f6522c375c09de10d22616c48a493841c4c
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
diff --git a/core/llvm_config.mk b/core/llvm_config.mk
index b870558..19fe790 100644
--- a/core/llvm_config.mk
+++ b/core/llvm_config.mk
@@ -71,6 +71,7 @@
   RS_TRIPLE := i686-unknown-linux
   CLANG_CONFIG_EXTRA_ASFLAGS += \
     -target i686-linux-android \
+    -msse3 \
     -nostdlibinc \
     -B$(TARGET_TOOLCHAIN_ROOT)/x86_64-linux-android/bin
   CLANG_CONFIG_EXTRA_CFLAGS += $(CLANG_CONFIG_EXTRA_ASFLAGS)