fix TryToFixInvalidVariablyModifiedType to reject negative array sizes

llvm-svn: 63557
diff --git a/clang/test/Sema/struct-decl.c b/clang/test/Sema/struct-decl.c
index cacd847..7d7961b 100644
--- a/clang/test/Sema/struct-decl.c
+++ b/clang/test/Sema/struct-decl.c
@@ -7,4 +7,5 @@
 
 struct foo {
 	char name[(int)&((struct bar *)0)->n];
+	char name2[(int)&((struct bar *)0)->n - 1]; //expected-error{{fields must have a constant size}}
 };