[SanitizerCoverage][NFC] Use appendToUsed instead of include

Summary:
Use appendToUsed instead of include to ensure that
SanitizerCoverage's constructors are not stripped.

Also, use isOSBinFormatCOFF() to determine if target
binary format is COFF.

Reviewers: pcc

Reviewed By: pcc

Subscribers: hiraditya

Differential Revision: https://reviews.llvm.org/D56369

llvm-svn: 351118