[llvm-c] Move LLVMAttributeIndex to a more apropriate place. NFC.

Author: deadalnix

llvm/include/llvm-c/Core.h

@@ -471,6 +471,8 @@ enum {
   LLVMAttributeFunctionIndex = -1,
 };
 
+typedef unsigned LLVMAttributeIndex;
+
 /**
  * Tail call kind for LLVMSetTailCallKind and LLVMGetTailCallKind.
  *
@@ -485,8 +487,6 @@ typedef enum {
   LLVMTailCallKindNoTail = 3,
 } LLVMTailCallKind;
 
-typedef unsigned LLVMAttributeIndex;
-
 enum {
   LLVMFastMathAllowReassoc = (1 << 0),
   LLVMFastMathNoNaNs = (1 << 1),