Support the 'a' length modifier in scanf format strings as a C90
extension.

This fixes gcc.dg/format/c90-scanf-3.c and ext-4.c (test for excess
errors).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146649 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed