[GISel]: Provide standard interface to observe changes in GISel passes

https://reviews.llvm.org/D54980

This provides a standard API across GISel passes to observe and notify
passes about changes (insertions/deletions/mutations) to MachineInstrs.
This patch also removes the recordInsertion method in MachineIRBuilder
and instead provides method to setObserver.

Reviewed by: vkeles.

llvm-svn: 348406
diff --git a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
index 6a8688f..02e787f 100644
--- a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
@@ -58,7 +58,8 @@
 
 bool MipsLegalizerInfo::legalizeCustom(MachineInstr &MI,
                                        MachineRegisterInfo &MRI,
-                                       MachineIRBuilder &MIRBuilder) const {
+                                       MachineIRBuilder &MIRBuilder,
+                                       GISelChangeObserver &Observer) const {
 
   using namespace TargetOpcode;