[PATCH 0/1] MR528: configure: Use AC_CHECK_FUNCS to define HAVE_GETTID

[Florian Weimer (＠fweimer)]

`VKD3D_CHECK_FUNC` does not use a fake prototype (`char gettid(void);`) and does not include `<unistd.h>`.  It always fails with Clang 16 and GCC 14 and other compilers which do not support implicit function declarations.

Related to:

* https://fedoraproject.org/wiki/Changes/PortingToModernC
* https://fedoraproject.org/wiki/Toolchain/PortingToModernC