Only build legacy plugins on mingw for now (again)

Signed-off-by: falkTX <falktx@falktx.com>

.travis/script.sh

@@ -5,9 +5,9 @@ set -e
 export DESTDIR=/tmp/distrho-ports
 
 if [ "${TARGET}" = "win32" ]; then
-    EXTRA_ARGS="--cross-file scripts/meson/win32.ini"
+    EXTRA_ARGS="--cross-file scripts/meson/win32.ini -Dbuild-legacy-only=true"
 elif [ "${TARGET}" = "win64" ]; then
-    EXTRA_ARGS="--cross-file scripts/meson/win64.ini"
+    EXTRA_ARGS="--cross-file scripts/meson/win64.ini -Dbuild-legacy-only=true"
 fi
 
 echo "meson build --buildtype=release ${EXTRA_ARGS}"