_FORTIFY_SOURCE: add memset / bzero support

Add _FORTIFY_SOURCE support for the following functions:

* memset
* bzero

Move the __BIONIC_FORTIFY_INLINE definition to cdefs.h so it
can be used from multiple header files.

Change-Id: Iead4d5e35de6ec97786d58ee12573f9b11135bb7
diff --git a/libc/Android.mk b/libc/Android.mk
index 596a856..70a5243 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -207,6 +207,7 @@
 	string/strxfrm.c \
 	string/__memcpy_chk.c \
 	string/__memmove_chk.c \
+	string/__memset_chk.c \
 	string/__strcat_chk.c \
 	string/__strcpy_chk.c \
 	string/__strncat_chk.c \