Fix static_assert feature detection on clang
Fix static_assert feature detection on clang

cppformat/cppformat,dean0x7d/cppformat,cppformat/cppformat,Jopie64/cppformat,mojoBrendan/fmt,mojoBrendan/fmt,dean0x7d/cppformat,alabuzhev/fmt,Jopie64/cppformat,dean0x7d/cppformat,lightslife/cppformat,alabuzhev/fmt,lightslife/cppformat,mojoBrendan/fmt,lightslife/cppformat,Jopie64/cppformat,cppformat/cppformat,alabuzhev/fmt