AMDGPU: Add a shader calling convention

This makes it possible to distinguish between mesa shaders
and other kernels even in the presence of compute shaders.

Patch By: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

Differential Revision: http://reviews.llvm.org/D18559

llvm-svn: 265589
diff --git a/llvm/test/CodeGen/AMDGPU/cayman-loop-bug.ll b/llvm/test/CodeGen/AMDGPU/cayman-loop-bug.ll
index c7b8c40..694d922 100644
--- a/llvm/test/CodeGen/AMDGPU/cayman-loop-bug.ll
+++ b/llvm/test/CodeGen/AMDGPU/cayman-loop-bug.ll
@@ -8,7 +8,7 @@
 ; CHECK-NOT: ALU_PUSH_BEFORE
 ; CHECK: END_LOOP
 ; CHECK: END_LOOP
-define void @main (<4 x float> inreg %reg0) #0 {
+define amdgpu_ps void @main (<4 x float> inreg %reg0) {
 entry:
   br label %outer_loop
 outer_loop:
@@ -28,5 +28,3 @@
 exit:
   ret void
 }
-
-attributes #0 = { "ShaderType"="0" }
\ No newline at end of file