Reintroduce the InlineHint function attribute.

This time it's for real! I am going to hook this up in the frontends as well.

The inliner has some experimental heuristics for dealing with the inline hint.
When given a -respect-inlinehint option, functions marked with the inline
keyword are given a threshold just above the default for -O3.

We need some experiments to determine if that is the right thing to do.

llvm-svn: 95466
diff --git a/llvm/include/llvm-c/Core.h b/llvm/include/llvm-c/Core.h
index 674dde5..98358fe 100644
--- a/llvm/include/llvm-c/Core.h
+++ b/llvm/include/llvm-c/Core.h
@@ -118,7 +118,8 @@
     LLVMNoCaptureAttribute  = 1<<21,
     LLVMNoRedZoneAttribute  = 1<<22,
     LLVMNoImplicitFloatAttribute = 1<<23,
-    LLVMNakedAttribute      = 1<<24
+    LLVMNakedAttribute      = 1<<24,
+    LLVMInlineHintAttribute = 1<<25
 } LLVMAttribute;
 
 typedef enum {