Add declare-spirv-builtins flag to libclc compilation.

This removes the need for forward declaring SPIR-V builtins in OpenCL
files.

Author: jchlanda

libclc/CMakeLists.txt

@@ -343,6 +343,10 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
 			set( opt_flags -O3 )
 		endif()
 
+                # Enable SPIR-V builtin function declarations, so they don't
+                # have to be explicity declared in the soruce.
+                list( APPEND flags -Xclang -fdeclare-spirv-builtins)
+
 		add_libclc_builtin_set(libspirv-${arch_suffix}
 			TRIPLE ${t}
 			TARGET_ENV libspirv

libclc/amdgcn/lib/mem_fence/fence.cl

@@ -1,8 +1,5 @@
 #include <clc/clc.h>
 
-_CLC_OVERLOAD _CLC_DEF void __spirv_MemoryBarrier(unsigned int memory,
-                                                  unsigned int semantics);
-
 // We don't have separate mechanism for read and write fences
 _CLC_DEF _CLC_OVERLOAD void read_mem_fence(cl_mem_fence_flags flags) {
   __spirv_MemoryBarrier(flags, 1);

libclc/amdgcn/lib/synchronization/barrier.cl

@@ -1,9 +1,5 @@
 #include <clc/clc.h>
 
-_CLC_OVERLOAD _CLC_DEF _CLC_CONVERGENT void
-__spirv_ControlBarrier(unsigned int scope, unsigned int memory,
-                       unsigned int semantics);
-
 _CLC_DEF _CLC_OVERLOAD void barrier(cl_mem_fence_flags flags) {
   // Call spir-v implementation of the barrier.
   // Set semantics to not None, so it performs mem fence.