MBEDTLS_PLATFORM_VSNPRINTF_ALT requires MBEDTLS_PLATFORM_C

mbedtls_vsnprintf replacement works like mbedtls_snprintf replacement, so
copy the requirements for MBEDTLS_PLATFORM_VSNPRINTF_ALT.

(MBEDTLS_PLATFORM_xxx_MACRO shouldn't require MBEDTLS_PLATFORM_C, but that's
a separate preexisting problem which I do not try address at this time.)

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index c0e0d30..6edd934 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2213,6 +2213,7 @@
     scripts/config.py unset MBEDTLS_PLATFORM_NV_SEED_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_PRINTF_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_SNPRINTF_ALT
+    scripts/config.py unset MBEDTLS_PLATFORM_VSNPRINTF_ALT
     scripts/config.py unset MBEDTLS_ENTROPY_NV_SEED
     scripts/config.py unset MBEDTLS_PLATFORM_C
     make CC=gcc CFLAGS='-Werror -O1' all test
@@ -2238,6 +2239,7 @@
     scripts/config.py unset MBEDTLS_PLATFORM_PRINTF_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_FPRINTF_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_SNPRINTF_ALT
+    scripts/config.py unset MBEDTLS_PLATFORM_VSNPRINTF_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_TIME_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_EXIT_ALT
     scripts/config.py unset MBEDTLS_PLATFORM_NV_SEED_ALT