Warn about non-standard format strings (pr12017)

This adds the -Wformat-non-standard flag (off by default,
enabled by -pedantic), which warns about non-standard
things in format strings (such as the 'q' length modifier,
the 'S' conversion specifier, etc.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151154 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/format-strings-c90.c b/test/Sema/format-strings-c90.c
index 0b32e82..63d5853 100644
--- a/test/Sema/format-strings-c90.c
+++ b/test/Sema/format-strings-c90.c
@@ -5,9 +5,8 @@
 int printf(const char *restrict, ...);
 
 void foo(char **sp, float *fp, int *ip) {
-  /* TODO: Warn that the 'a' length modifier is an extension. */
-  scanf("%as", sp);
-  scanf("%a[abc]", sp);
+  scanf("%as", sp); /* expected-warning{{'a' is a non-standard length modifier}} */
+  scanf("%a[abc]", sp); /* expected-warning{{'a' is a non-standard length modifier}} */
 
   /* TODO: Warn that the 'a' conversion specifier is a C99 feature. */
   scanf("%a", fp);
@@ -21,7 +20,11 @@
   scanf("%da", ip);
 
   /* Test argument type check for the 'a' length modifier. */
-  scanf("%as", fp); /* expected-warning{{format specifies type 'char **' but the argument has type 'float *'}} */
-  scanf("%aS", fp); /* expected-warning{{format specifies type 'wchar_t **' (aka 'int **') but the argument has type 'float *'}} */
-  scanf("%a[abc]", fp); /* expected-warning{{format specifies type 'char **' but the argument has type 'float *'}} */
+  scanf("%as", fp); /* expected-warning{{format specifies type 'char **' but the argument has type 'float *'}}
+                       expected-warning{{'a' is a non-standard length modifier}} */
+  scanf("%aS", fp); /* expected-warning{{format specifies type 'wchar_t **' (aka 'int **') but the argument has type 'float *'}}
+                       expected-warning{{'a' is a non-standard length modifier}}
+                       expected-warning{{'S' is a non-standard conversion specifier}} */
+  scanf("%a[abc]", fp); /* expected-warning{{format specifies type 'char **' but the argument has type 'float *'}}
+                           expected-warning{{'a' is a non-standard length modifier}} */
 }