[OpenMP] Remove declaration and usage of __AMDGCN_WAVEFRONT_SIZE (#143761)

Removes usage of __AMDGCN_WAVEFRONT_SIZE as compile time constant.

---------

Co-authored-by: Shilei Tian <i@tianshilei.me>

openmp/runtime/src/include/ompx.h.var

@@ -9,13 +9,21 @@
 #ifndef __OMPX_H
 #define __OMPX_H
 
-#ifdef __AMDGCN_WAVEFRONT_SIZE
-#define __WARP_SIZE __AMDGCN_WAVEFRONT_SIZE
-#else
-#define __WARP_SIZE 32
+#if (defined(__NVPTX__) || defined(__AMDGPU__))
+#include <gpuintrin.h>
+#define __OMPX_TARGET_IS_GPU
 #endif
 
 typedef unsigned long uint64_t;
+typedef unsigned int uint32_t;
+
+static inline uint32_t __warpSize(void) {
+#ifdef __OMPX_TARGET_IS_GPU
+  return __gpu_num_lanes();
+#else
+  __builtin_trap();
+#endif
+}
 
 #ifdef __cplusplus
 extern "C" {
@@ -212,7 +220,7 @@ static inline uint64_t ballot_sync(uint64_t mask, int pred) {
 ///{
 #define _TGT_KERNEL_LANGUAGE_SHFL_DOWN_SYNC(TYPE, TY)                          \
   static inline TYPE shfl_down_sync(uint64_t mask, TYPE var, unsigned delta,   \
-                                    int width = __WARP_SIZE) {                 \
+                                    int width = __warpSize()) {                \
     return ompx_shfl_down_sync_##TY(mask, var, delta, width);                  \
   }