This is needed to work around a build failure when this test fails, as
it spuriously does when cross-compiling for MinGW using v10 API package,
see https://sourceforge.net/p/mingw-w64/bugs/935/ for more details.
Of course, the fact that the build fails if snprintf() is unavailable is
actually a bug, but in practice this function is available everywhere by
now, so simply stop testing for it.
This mostly cherry picks ceff22ee (Use C99 snprintf, 2021-01-31), but
keeps the test for MSVC versions without vsnprintf() for compatibility.
libtiff mailing list on Mon, 22 Jun 2015 21:21:01 +0100. Several
corrections to ensure that the autotools build still works were
added by me. I have not yet tested the build using 'cmake' or
MSVC with 'nmake'.
