util: drop strncat(), strcmp(), strncmp(), snprintf() & vsnprintf() MSVC fallbacks

util: drop strncat(), strcmp(), strncmp(), snprintf() & vsnprintf() MSVC fallbacks

It would seem MSVC>=2015 is now C99-compliant wrt these functions:
strncat:   https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strncat-strncat-l-wcsncat-wcsncat-l-mbsncat-mbsncat-l?view=vs-2017
strcmp:    https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strcmp-wcscmp-mbscmp?view=vs-2017
strncmp:   https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strncmp-wcsncmp-mbsncmp-mbsncmp-l?view=vs-2017
snprintf:  https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/snprintf-snprintf-snprintf-l-snwprintf-snwprintf-l?view=vs-2017
vsnprintf: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/vsnprintf-vsnprintf-vsnprintf-l-vsnwprintf-vsnwprintf-l?view=vs-2017

Suggested-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>