gen-lockedsig-cache: ensure symlinks are dereferenced

If you set up a local mirror in SSTATE_MIRRORS then you can end up with
symlinks in SSTATE_DIR rather than real files. We don't want these
symlinks in the sstate-cache prodcued by gen-lockedsig-cache, so
dereference any symlinks before copying.

(From OE-Core rev: d65a6ee9e7a9c63b9a16bdb5025af8a7c6433c4f)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/gen-lockedsig-cache

@@ -57,13 +57,14 @@ for f in files:
     destdir = os.path.dirname(dst)
     mkdir(destdir)
 
+    src = os.path.realpath(f)
     if os.path.exists(dst):
         os.remove(dst)
-    if (os.stat(f).st_dev == os.stat(destdir).st_dev):
+    if (os.stat(src).st_dev == os.stat(destdir).st_dev):
         print('linking')
-        os.link(f, dst)
+        os.link(src, dst)
     else:
         print('copying')
-        shutil.copyfile(f, dst)
+        shutil.copyfile(src, dst)
 
 print('Done!')