Add more constraint registers for mips.

Patch by Jack Carter. Testcase cleanup by me.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153921 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index eacdf5e..1fcef33 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -3522,6 +3522,9 @@
     case 'd': // Equivalent to "r" unless generating MIPS16 code.
     case 'y': // Equivalent to "r", backwards compatibility only.
     case 'f': // floating-point registers.
+    case 'c': // $25 for indirect jumps
+    case 'l': // lo register
+    case 'x': // hilo register pair
       Info.setAllowsRegister();
       return true;
     }