The current git master version of mingw-w64 activates
__USE_MINGW_ANSI_STDIO by default if targeting C99 (which is the
default C version in both GCC and Clang), unless using UCRT.

This patch (a backport of ca6f6cfbb4c78c063f2a50bb758edfc95c9d64a2
from gettext git) fixes building gettext when __USE_MINGW_ANSI_STDIO
is enabled - i.e. fixing building gettext with latest mingw-w64 when
using msvcrt.dll.