ARM: raise error message when complex SO expressions can't really be
solved as a constant at compilation time.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204898 91177308-0d34-0410-b5e6-96231b3b80d8
Fix for pr18931: Crash using integrated assembler with immediate arithmetic

Fix description:
Expressions like 'cmp r0, #(l1 - l2) >> 3' could not be evaluated on asm parsing stage,
since it is impossible to resolve labels on this stage. In the end of stage we still have
expression (MCExpr).
Then, when we want to encode it, we expect it to be an immediate, but it still an expression.
Patch introduces a Fixup (MCFixup instance), that is processed after main encoding stage.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204899 91177308-0d34-0410-b5e6-96231b3b80d8