[libomptarget][nfc] Replace static const with enum

[JonChesterfield]

Summary

[libomptarget][nfc] Replace static const with enum

Semantically identical. Replaces 0xff... with ~0 to spare counting the f.
Has the advantage that the compiler doesn't need to prove the 4/8 byte
value dead before discarding it, and sidesteps the compilation question
associated with what static means for a single source language.

[jdoerfert]

LGTM

openmp/libomptarget/deviceRTLs/amdgcn/src/target_impl.h

INLINE void __kmpc_impl_unpack(uint64_t val, uint32_t &lo, uint32_t &hi) {
   lo = (uint32_t)(val & UINT64_C(0x00000000FFFFFFFF));
   hi = (uint32_t)((val & UINT64_C(0xFFFFFFFF00000000)) >> 32);
 }
 
 INLINE uint64_t __kmpc_impl_pack(uint32_t lo, uint32_t hi) {
   return (((uint64_t)hi) << 32) | (uint64_t)lo;
 }
 
-static const __kmpc_impl_lanemask_t __kmpc_impl_all_lanes =
-    UINT64_C(0xffffffffffffffff);
+enum : __kmpc_impl_lanemask_t {
+  __kmpc_impl_all_lanes = ~(__kmpc_impl_lanemask_t)0
+};
 
 DEVICE __kmpc_impl_lanemask_t __kmpc_impl_lanemask_lt();
 
 DEVICE __kmpc_impl_lanemask_t __kmpc_impl_lanemask_gt();
 
 DEVICE uint32_t __kmpc_impl_smid();
 
 DEVICE double __kmpc_impl_get_wtick();

openmp/libomptarget/deviceRTLs/nvptx/src/target_impl.h

 }
 
 INLINE uint64_t __kmpc_impl_pack(uint32_t lo, uint32_t hi) {
   uint64_t val;
   asm volatile("mov.b64 %0, {%1,%2};" : "=l"(val) : "r"(lo), "r"(hi));
   return val;
 }
 
-static const __kmpc_impl_lanemask_t __kmpc_impl_all_lanes =
-    UINT32_C(0xffffffff);
+enum : __kmpc_impl_lanemask_t {
+  __kmpc_impl_all_lanes = ~(__kmpc_impl_lanemask_t)0
+};
 
 INLINE __kmpc_impl_lanemask_t __kmpc_impl_lanemask_lt() {
   __kmpc_impl_lanemask_t res;
   asm("mov.u32 %0, %%lanemask_lt;" : "=r"(res));
   return res;
 }
 
 INLINE __kmpc_impl_lanemask_t __kmpc_impl_lanemask_gt() {