Add a temporary hack to work around __NDK_FPABI__.

Test: make checkbuild
Bug: http://b/27533932
Change-Id: I0262eed91b10b0dd5fe27a61fb8f35b3c062280e

libc/include/sys/cdefs.h

@@ -353,4 +353,17 @@ int __size_mul_overflow(__SIZE_TYPE__ a, __SIZE_TYPE__ b, __SIZE_TYPE__ *result)
 }
 #endif
 
+/*
+ * TODO(danalbert): Remove this once we've moved entirely off prebuilts/ndk.
+ *
+ * The NDK used to have a __NDK_FPABI__ that was defined to empty for most cases
+ * but `__attribute__((pcs("aapcs")))` for the now defunct armeabi-v7a-hard ABI.
+ *
+ * During the transition from prebuilts/ndk to ndk_headers, we'll have some
+ * headers that still use __NDK_FPABI__ while the libc headers have stopped
+ * defining it. In the interim, just provide an empty definition to keep the
+ * build working.
+ */
+#define __NDK_FPABI__
+
 #endif /* !_SYS_CDEFS_H_ */