[mips] Manually replace JAL pseudo-instructions with their JALR equivalent,...

[mips] Manually replace JAL pseudo-instructions with their JALR equivalent, instead of using InstAlias.

Summary:
This is needed by the .cprestore assembler directive.

This directive needs to be able to insert an LW instruction after every JALR replacement of a JAL pseudo-instruction
(and never after a JALR which has NOT been a result of a pseudo-instruction replacement).

The problem with using InstAlias for these is that after it replaces the pseudo-instruction, we can't find out if the resulting JALR instruction
was generated by an InstAlias or not, so we don't know whether or not to insert our LW instruction.

By replacing it manually, we know when the pseudo-instruction replacement happens and we can insert the LW instruction correctly.

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: emaste, llvm-commits

Differential Revision: http://reviews.llvm.org/D5601

llvm-svn: 227568