Fix greedy FileCheck expression in test/Driver/mips-abi.c

Fix greedy FileCheck expression in test/Driver/mips-abi.c

'ld{{.*}}"' seems to match the complete line for me which is failing
the test. Only allow an optional '.exe' for Windows systems as most
other tests do.
Another possibility would be to collapse the greedy expression with
the next check to avoid matching the full line.

Differential Revision: https://reviews.llvm.org/D52619

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@343240 91177308-0d34-0410-b5e6-96231b3b80d8