Introduce Target::createNullTargetStreamer and use it from IRObjectFile.

A null MCTargetStreamer allows IRObjectFile to ignore target-specific
directives. Previously we were crashing.

Differential Revision: http://reviews.llvm.org/D7711

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229797 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed