[libclc] Implement __clc_get_local_size/__clc_get_max_sub_group_size for amdgcn (#153785)

This simplifies downstream refactoring of libspirv workitem function in
https://github.com/intel/llvm/tree/sycl/libclc/libspirv/lib/generic

libclc/clc/lib/amdgcn/SOURCES

@@ -5,4 +5,6 @@ workitem/clc_get_global_offset.cl
 workitem/clc_get_global_size.cl
 workitem/clc_get_group_id.cl
 workitem/clc_get_local_id.cl
+workitem/clc_get_local_size.cl
+workitem/clc_get_max_sub_group_size.cl
 workitem/clc_get_work_dim.cl

libclc/clc/lib/amdgcn/workitem/clc_get_local_size.cl

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <clc/workitem/clc_get_local_size.h>
+
+_CLC_OVERLOAD _CLC_DEF size_t __clc_get_local_size(uint dim) {
+  switch (dim) {
+  case 0:
+    return __builtin_amdgcn_workgroup_size_x();
+  case 1:
+    return __builtin_amdgcn_workgroup_size_y();
+  case 2:
+    return __builtin_amdgcn_workgroup_size_z();
+  default:
+    return 1;
+  }
+}

libclc/clc/lib/amdgcn/workitem/clc_get_max_sub_group_size.cl

@@ -0,0 +1,13 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <clc/workitem/clc_get_max_sub_group_size.h>
+
+_CLC_OVERLOAD _CLC_DEF uint __clc_get_max_sub_group_size() {
+  return __builtin_amdgcn_wavefrontsize();
+}