tools/autobuild: Don't use "-B" for make, it's already a fresh build.

And using "-B" means mpy-cross is forcefully rebuilt, sometimes with
invalid CFLAGS_EXTRA options which makes the auto-build fail.
Signed-off-by: Damien George <damien@micropython.org>

tools/autobuild/build-cc3200-latest.sh

@@ -8,7 +8,7 @@ function do_build() {
     shift
     echo "building $descr $board"
     build_dir=/tmp/cc3200-build-$board
-    $MICROPY_AUTOBUILD_MAKE -B $@ BTARGET=application BOARD=$board BUILD=$build_dir || exit 1
+    $MICROPY_AUTOBUILD_MAKE $@ BTARGET=application BOARD=$board BUILD=$build_dir || exit 1
     zip $dest_dir/$descr$fw_tag.zip $build_dir/mcuimg.bin
     rm -rf $build_dir
 }

tools/autobuild/build-stm32-latest.sh

@@ -8,7 +8,7 @@ function do_build() {
     shift
     echo "building $descr $board"
     build_dir=/tmp/stm-build-$board
-    $MICROPY_AUTOBUILD_MAKE -B $@ BOARD=$board BUILD=$build_dir || exit 1
+    $MICROPY_AUTOBUILD_MAKE $@ BOARD=$board BUILD=$build_dir || exit 1
     mv $build_dir/firmware.dfu $dest_dir/$descr$fw_tag.dfu
     rm -rf $build_dir
 }