MSVC optimizations for count_digits. (#1890)
MSVC optimizations for count_digits. (#1890)

Changed the clz implementations to use xor instead of subtraction so that when
count_digits "undoes" the BSR -> CLZ translation, the optimizer is more
willing to recognize the equivalence.
Changed the data array in bsr2log10 to static since otherwise MSVC generates
code to build the array every time the function is called.
alabuzhev/fmt,alabuzhev/fmt,alabuzhev/fmt,cppformat/cppformat,cppformat/cppformat,cppformat/cppformat