[mips] Use "or $r0, $r1, $zero" instead of "addu $r0, $zero, $r1" to copy

physical register $r1 to $r0.

GNU disassembler recognizes an "or" instruction as a "move", and this change
makes the disassembled code easier to read.

Original patch by Reed Kotler.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170655 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/Mips/gpreg-lazy-binding.ll

@@ -2,10 +2,10 @@
 
 @g = external global i32
 
-; CHECK:     addu  $gp
+; CHECK:     or    $gp
 ; CHECK:     jalr  $25
 ; CHECK:     nop
-; CHECK-NOT: addu  $gp
+; CHECK-NOT: or    $gp
 ; CHECK:     jalr  $25
 
 define void @f0() nounwind {