tools/autobuild: Use distinct directory for building stm32 variants.

Previous the build directory just used the board name, now make it use the
variant name too.

This shouldn't have any change because the existing directory should not
exist (all builds run by these scripts remove their build directory after
completion), but it makes debugging easier.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tools/autobuild/build-stm32-extra.sh

@@ -10,7 +10,7 @@ function do_build() {
     for variant in `$MICROPY_AUTOBUILD_MAKE BOARD=$board query-variants | grep VARIANTS: | cut -d' ' -f2-`; do
         target=$descr-$variant
         echo "building $target $board"
-        build_dir=/tmp/stm-build-$board
+        build_dir=/tmp/stm-build-$board-$variant
         $MICROPY_AUTOBUILD_MAKE $@ BOARD=$board BOARD_VARIANT=$variant BUILD=$build_dir || exit 1
         mv $build_dir/firmware.dfu $dest_dir/$target$fw_tag.dfu
         mv $build_dir/firmware.hex $dest_dir/$target$fw_tag.hex