Use builtin_clz for clang on windows

[OetkenPurveyorOfCode]

Clang on windows defines both _MSC_VER and clang for compatibility reason. The logic in sinfl.h selects the MSVC buitlin which clang only understands in clang-cl compatibility mode. If compiled with regular clang _MSC_VER is defined but the _BitScanReverse builtin is not recognised. This leads to the following warning during compilation:

In file included from ../raylib/src\rcore.c:141:
../raylib/src/external/sinfl.h:175:19: warning: incompatible pointer types passing 'unsigned int *' to parameter of type
      'unsigned long *' [-Wincompatible-pointer-types]
  175 |   _BitScanReverse(&n, n);
      |                   ^~

This PR fixes that by selecting the __builtin_clz builtin if clang is defined.

[raysan5]

@OetkenPurveyorOfCode Thanks for the review! Please note that sinfl.h is actually an external library, it should probably also be fixed on base repo: https://github.com/vurtun/lib/blob/master/sinfl.h