Temporarily force standard *printf functions on MingW

On MingW, temporarily force the use of the standard versions of `snprintf()`
and `vsnprintf()` (since we set `__USE_MINGW_ANSI_STDIO` in
`mbedtls_platform_requirements.h`). Do not honor `platform.h` configuration,
because with the current TF-PSA-Crypto, `MBEDTLS_PLATFORM_VSNPRINTF_ALT and
`MBEDTLS_PLATFORM_SNPRINTF_ALT` are always enabled on MinGW, so what matters
is the setting of `__USE_MINGW_ANSI_STDIO` when `platform.c` is built, and
until https://github.com/Mbed-TLS/TF-PSA-Crypto/pull/694, the legacy printf
functions are used there.

Revert this commit once the `tf-psa-crypto` module is updated with the merge
of https://github.com/Mbed-TLS/TF-PSA-Crypto/pull/694.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/debug.c

@@ -21,6 +21,20 @@
 /* DEBUG_BUF_SIZE must be at least 2 */
 #define DEBUG_BUF_SIZE      512
 
+/* Temporary hack: on MingW, do not honor the platform.h configuration
+ * for snprintf and vsnprintf. Instead, force the native functions,
+ * which are the standard ones, not the Windows legacy ones.
+ *
+ * This hack should be removed once TF-PSA-Crypto has been updated to
+ * use the standard printf family.
+ */
+#if defined(__MINGW32__)
+#undef mbedtls_snprintf
+#define mbedtls_snprintf snprintf
+#undef mbedtls_vsnprintf
+#define mbedtls_vsnprintf vsnprintf
+#endif
+
 int mbedtls_debug_snprintf(char *dest, size_t maxlen,
                            const char *format, ...)
 {