Disable clang optimization that has segmentation fault.

When compiling for aosp_fugu-userdebug, clang aborted in pass:

  Running pass 'Function Pass Manager' on module 'system/core/libmincrypt/p256_ec.c'.
  Running pass 'X86 DAG->DAG Instruction Selection' on function '@felem_square'

BUG: 18790528
Change-Id: I416c07cae4c1a9743655bc45bd33c10a5cc9b41f
diff --git a/Android.mk b/Android.mk
index 7906986..503bcb4 100644
--- a/Android.mk
+++ b/Android.mk
@@ -6,6 +6,8 @@
 LOCAL_MODULE := libmincrypt
 LOCAL_SRC_FILES := dsa_sig.c p256.c p256_ec.c p256_ecdsa.c rsa.c sha.c sha256.c
 LOCAL_CFLAGS := -Wall -Werror
+# Clang's slp-vectorize phase has segmentation fault when compiling p256_ec.c.
+LOCAL_CLANG_CFLAGS += -fno-slp-vectorize
 include $(BUILD_STATIC_LIBRARY)
 
 include $(CLEAR_VARS)