Use binary write mode in WriteToFile function to avoid appended \r characters on Windows

Summary:
When using libfuzzer on Windows, in the contents of a crash sample, bytes that can be mistaken for a \n are replaced by a \r\n sequence. As a consequence, crashes are not reproducible. This patch will open files in binary mode to fix this issue. The patch does not affect POSIX systems.

Patch by tuktuk

Reviewers: kcc, vitalybuka

Reviewed By: vitalybuka

Subscribers: dexonsmith, jdoerfert, llvm-commits, #sanitizers

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D60008

llvm-svn: 357807