FORTIFY_SOURCE: add sprintf / vsprintf support

sprintf FORTIFY_SOURCE protections are not available
on clang.

Also add various __attribute__s to stdio functions.

Change-Id: I936d1f9e55fe53a68885c4524b7b59e68fed218d
diff --git a/libc/Android.mk b/libc/Android.mk
index c507457..f90520e 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -141,7 +141,9 @@
 	stdio/wbuf.c \
 	stdio/wsetup.c \
 	stdio/__snprintf_chk.c \
+	stdio/__sprintf_chk.c \
 	stdio/__vsnprintf_chk.c \
+	stdio/__vsprintf_chk.c \
 	stdlib/_rand48.c \
 	stdlib/assert.c \
 	stdlib/atexit.c \