common-source: fix create-spdx handling

- do_create_spdx does have to wait till the shared source
  tree is properly populated
- override the spdx class code detection to determine
  if sources are under work-shared.
  the core code does only look at WORKDIR, which isn’t
  overridden in every case, more likely only S and B are
  touched, which make the spdx class code assume that
  these are per-workdir sources and starts to remove the
  shared sources via bitbake’s cleandirs settings.
  Avoid that by let the code always handle recipes including
  common-source as shared sources.

Relates to kraj#721

Signed-off-by: Konrad Weihmann <kweihmann@witekio.com>

recipes-devtools/clang/common-source.inc

@@ -9,3 +9,9 @@ SRC_URI = ""
 
 do_configure[depends] += "llvm-project-source-${PV}:do_patch"
 do_populate_lic[depends] += "llvm-project-source-${PV}:do_unpack"
+do_create_spdx[depends] += "llvm-project-source-${PV}:do_patch"
+
+# spdx shared workdir detection fails as not WORKDIR is altered but S and B
+# return always true to fix that
+def is_work_shared_spdx(d):
+    return True