Fixed unknown pragma warnings for _BitScanReverse.
Fixed unknown pragma warnings for _BitScanReverse.

Changed to only define the MSVC implementations for clz and clzll if the builtins are not available to avoid warnings about an unknown #pragma for "intrinsic".

cppformat/cppformat,mojoBrendan/fmt,dean0x7d/cppformat,lightslife/cppformat,cppformat/cppformat,cppformat/cppformat,alabuzhev/fmt,alabuzhev/fmt,mojoBrendan/fmt,dean0x7d/cppformat,lightslife/cppformat,mojoBrendan/fmt,lightslife/cppformat,alabuzhev/fmt,dean0x7d/cppformat