Set hasSideEffects=0 for TargetOpcode::{CFI_INSTRUCTION,EH_LABEL,GC_LABEL,ANNOTATION_LABEL}

D37065 (committed as rL317674) explicitly set hasSideEffects for all 
TargetOpcode::* instructions where it was inferred previously. This is a 
follow-up to that patch, setting hasSideEffects=0 for CFI_INSTRUCTION, 
EH_LABEL, GC_LABEL and ANNOTATION_LABEL. All LLVM tests pass after this 
change.

This patch also modifies MachineInstr::isLabel returns true for a 
TargetOpcode::ANNOTATION_LABEL, which ensures that an annotation label won't 
be incorrectly considered safe to move.

Differential Revision: https://reviews.llvm.org/D39941

llvm-svn: 318174