message: Change latest supported LLVM to 14.0 for ISPC v1.18.0 release
diff: #define ISPC_LLVM_15_0 150000
  #define OLDEST_SUPPORTED_LLVM ISPC_LLVM_10_0
  -#define LATEST_SUPPORTED_LLVM ISPC_LLVM_15_0
  +#define LATEST_SUPPORTED_LLVM ISPC_LLVM_14_0
  #ifdef __ispc__xstr
  #undef __ispc__xstr
  