Revert "build: reserve `--color-diagnostics` for lld"
This reverts SVN r330158.
Seems that there was a change to linker flags handling in SVN r316972.
That would alter the behaviour to correct the linker flag handling in
CMake (requiring CMake 3.4.3+). Since that is already the minimum
version required for LLVM, hard coding the knowledge of the linker is
not required, which is a strictly better solution.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330161
91177308-0d34-0410-b5e6-
96231b3b80d8