kbuild: dummy-tools: avoid tmpdir leak in dummy gcc

kbuild: dummy-tools: avoid tmpdir leak in dummy gcc

BugLink: https://bugs.launchpad.net/bugs/1990564
commit aac289653fa5adf9e9985e4912c1d24a3e8cbab2 upstream.

When passed -print-file-name=plugin, the dummy gcc script creates a
temporary directory that is never cleaned up. To avoid cluttering
$TMPDIR, instead use a static directory included in the source tree.

Fixes: 76426e238834 ("kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>