sysmocom-archiver: whitelist gcc-cross

* archiver discard the source providing
  for all native and shared-work recipes,
  so we whitelist gcc-cross, which covers
  the source code for the runtime libgcc
  package

Fixes: SYS#372

classes/sysmocom-archiver.bbclass

@@ -113,6 +113,9 @@ def not_tarball(d):
     workdir = d.getVar('WORKDIR',True)
     s = d.getVar('S',True)
     if 'work-shared' in s or 'task-' in workdir or 'native' in workdir:
+        pn = bb.data.getVar('PN', d , True)
+        if pn == 'gcc-cross':
+              return False
         return True
     else:
         return False