Fix massive resource leaks in the bytecode reader. Reading a bytecode file

with ParseBytecodeFile used to leak both a ModuleProvider (and related
bytecode parser stuff attached to it) AND a file descriptor, which was
never closed.  This prevented gccld/llvm-ld/llvm-link from linking together
apps with more that ~252 .bc files on darwin.

llvm-svn: 30912