Instead of crashing when MCAsmInfo is NULL, add an assert.

This helps with porting code from 2.9 to 3.0 as TargetSelect.h changed location,
and if you include the old one by accident you will trigger this assert.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140848 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed