Properly handle short file names on the command line in Windows

Some build systems use the short (8.3) file names on Windows, especially if the path has spaces in it. The shortening made it impossible for clang to distinguish between clang.exe, clang++.exe, and clang-cl.exe.  So this expands short names in the first argument and does wildcard expansion for the rest.

Differential Revision: http://reviews.llvm.org/D21420

llvm-svn: 272967