Temporarily revert "Change -gz and -Wa,--compress-debug-sections to use gABI...

Temporarily revert "Change -gz and -Wa,--compress-debug-sections to use gABI compression (SHF_COMPRESSED)"

This affects users of older (pre 2.26) binutils in such a way that they can't necessarily
work around it as it doesn't support the compress option on the command line. Reverting
to unblock them and we can revisit whether to make this change now or fix how we want
to express the option.

This reverts commit bdb21337/r360403.

llvm-svn: 360703