Guard fortify inlines with __ANDROID_API__.

Test: make checkbuild with libc ndk_library patches applied
Change-Id: Ic5e248994c4f2702b0f4d6dfeda787187ea86017
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 03effcd..1bbd669 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -266,6 +266,7 @@
 
 #if defined(__BIONIC_FORTIFY)
 
+#if __ANDROID_API__ >= 17
 __BIONIC_FORTIFY_INLINE
 __printflike(3, 0) int vsnprintf(char* dest, size_t size, const char* _Nonnull format, __va_list ap) {
     return __builtin___vsnprintf_chk(dest, size, 0, __bos(dest), format, ap);
@@ -299,7 +300,9 @@
     return __builtin___sprintf_chk(dest, 0, __bos(dest), format, __builtin_va_arg_pack());
 }
 #endif
+#endif /* __ANDROID_API__ >= 17 */
 
+#if __ANDROID_API__ >= 24
 __BIONIC_FORTIFY_INLINE
 size_t fread(void * __restrict buf, size_t size, size_t count, FILE * __restrict stream) {
     size_t bos = __bos0(buf);
@@ -351,6 +354,7 @@
 
     return __fwrite_chk(buf, size, count, stream, bos);
 }
+#endif /* __ANDROID_API__ >= 24 */
 
 #if !defined(__clang__)