[SystemZ] Utilize Test Data Class instructions.

This adds a new SystemZ-specific intrinsic, llvm.s390.tdc.f(32|64|128),
which maps straight to the test data class instructions.  A new IR pass
is added to recognize instructions that can be converted to TDC and
perform the necessary replacements.

Differential Revision: http://reviews.llvm.org/D21949

llvm-svn: 275016