[Support] Use FILE_SHARE_DELETE to fix RemoveFileOnSignal on Windows

Summary:
Tools like clang that use RemoveFileOnSignal on their output files
weren't actually able to clean up their outputs before this change.  Now
the call to llvm::sys::fs::remove succeeds and the temporary file is
deleted. This is a stop-gap to fix clang before implementing the
solution outlined in PR34070.

Reviewers: davide

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D36337

llvm-svn: 310137