gcc-source: Fix racing on building gcc-source-14.2.0 and lib32-gcc-source-14.2.0

gcc-source: Fix racing on building gcc-source-14.2.0 and lib32-gcc-source-14.2.0

While enabling multilib, build gcc-source-14.2.0 and lib32-gcc-source-14.2.0
at the same time:

    $ MACHINE = "qemux86-64"
    $ require conf/multilib.conf
    $ MULTILIBS = "multilib:lib32"
    $ DEFAULTTUNE:virtclass-multilib-lib32 = "x86"
    $ bitbake gcc-source-14.2.0 lib32-gcc-source-14.2.0
    ...
    $ cat tmp-glibc/work-shared/gcc-14.2.0-r0.vr2401/temp/log.task_order
    20241012-064533.415426 do_recipe_qa (2688052): log.do_recipe_qa.2688052
    20241012-064533.463783 do_recipe_qa (2688051): log.do_recipe_qa.2688051
    20241012-064533.805164 do_fetch (2688257): log.do_fetch.2688257
    20241012-064533.852955 do_fetch (2688256): log.do_fetch.2688256
    20241012-064617.823714 do_unpack (2698542): log.do_unpack.2698542
    20241012-064617.871730 do_unpack (2698541): log.do_unpack.2698541
    ...

There are two tasks for do_fetch, do_unpack and others, so there are race issues.

Both of them have the same hardcode 'gcc' prefix in ${WORKDIR} and
${S}, explicitly disable lib32-gcc-source-14.2.0 for multilib

Set gcc-source as BPN of gcc-source-14.2.0

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>