Fix buildcache relocate: only skip if rpaths are relative (#7605)

This fixes a check that decides when to skip buildcache relocation.
Originally the check was flawed in two ways: it would skip if the
source prefix matched the destination prefix, which no longer
matters since the source prefix is replaced with a placeholder
(so it always needs to be updated); it also would skip relocation
if the rpaths were not relative, when in fact it should be the
opposite (binaries without relative rpaths *should* be relocated,
and those without don't need it).

lib/spack/spack/binary_distribution.py

@@ -415,7 +415,7 @@ def relocate_package(workdir, allow_root):
     new_path = spack.store.layout.root
     old_path = buildinfo['buildpath']
     rel = buildinfo.get('relative_rpaths', False)
-    if new_path == old_path and not rel:
+    if rel:
         return
 
     tty.msg("Relocating package from",