Update changelog to call out MinGW

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>

ChangeLog.d/fix-msvc-version-guard-format-zu.txt

 Bugfix
    * Fix definition of MBEDTLS_PRINTF_SIZET to prevent runtime crashes that
      occurred whenever SSL debugging was enabled on a copy of Mbed TLS built
-     with Visual Studio 2013.
+     with Visual Studio 2013 or MinGW.
      Fixes #10017.