Fix racing on building lib32-llvm-project-source-19.1.0 and llvm-project-source-19.1.0

[hongxu-jia]

While enabling multilib, build lib32-llvm-project-source-19.1.0 and llvm-project-source-19.1.0 at the same time:

$ MACHINE = "qemux86-64"
$ require conf/multilib.conf
$ MULTILIBS = "multilib:lib32"
$ DEFAULTTUNE:virtclass-multilib-lib32 = "x86"
$ bitbake lib32-llvm-project-source-19.1.0 llvm-project-source-19.1.0
...
$ cat tmp/work-shared/llvm-project-source-19.1.0-r0/temp/log.task_order
20241012-070604.819630 do_recipe_qa (2728706): log.do_recipe_qa.2728706
20241012-070604.883194 do_recipe_qa (2728707): log.do_recipe_qa.2728707
20241012-070605.037448 do_fetch (2728779): log.do_fetch.2728779
20241012-070605.165280 do_fetch (2728848): log.do_fetch.2728848
20241012-071030.798104 do_unpack (2733554): log.do_unpack.2733554
20241012-071030.864536 do_unpack (2733559): log.do_unpack.2733559

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

Both of them have the same hardcode 'llvm-project-source-' prefix in ${WORKDIR} and ${S}, explicitly disable lib32-llvm-project-source-19.1.0 for multilib

Set llvm-project-source as BPN of llvm-project-source-19.1.0

---

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[kraj]

lgtm