[Solaris] Detect Solaris LD, use detection results to pass Solaris-ld options

Solaris ld is not the only linker available on Solaris.
Introducing linker detection and using LLVM_LINKER_IS_SOLARISLD to
select Solaris-ld specific handling.

Patch by: Fedor Sergeev

Differential Revision: https://reviews.llvm.org/D35325

llvm-svn: 307852