Add -Oz option and use it to set the inline threshold to 25.
Radar 9333566.  Patch by Chad Rosier!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130554 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/BackendUtil.cpp b/lib/CodeGen/BackendUtil.cpp
index 9bd4bfd..497ccc5 100644
--- a/lib/CodeGen/BackendUtil.cpp
+++ b/lib/CodeGen/BackendUtil.cpp
@@ -134,8 +134,10 @@
     //
     // FIXME: Derive these constants in a principled fashion.
     unsigned Threshold = 225;
-    if (CodeGenOpts.OptimizeSize)
+    if (CodeGenOpts.OptimizeSize == 1) //-Os
       Threshold = 75;
+    else if (CodeGenOpts.OptimizeSize == 2) //-Oz
+      Threshold = 25;
     else if (OptLevel > 2)
       Threshold = 275;
     InliningPass = createFunctionInliningPass(Threshold);