gen-lockedsig-cache: Allow cross-filesystem copies.

Since this previously always tried to use hardlinks you couldn't have
the source and destination be on different devices. This change allows
for that and also prevents failure in situations where the files already
existed.

(From OE-Core rev: cf675896340ebed7c4830b93d791ddb08999031f)

Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/gen-lockedsig-cache

@@ -35,6 +35,12 @@ for s in sigs:
 
 for f in files:
     dst = f.replace(sys.argv[2], sys.argv[3])
-    mkdir(os.path.dirname(dst))
-    os.link(f, dst)
+    destdir = os.path.dirname(dst)
+    mkdir(destdir)
 
+    if os.path.exists(dst):
+        os.remove(dst)
+    if (os.stat(f).st_dev == os.stat(destdir).st_dev):
+        os.link(f, dst)
+    else:
+        shutil.copyfile(f, dst)