Implement better scanning of source file dependencies - library source files are now only selected as a dependency if the included header declares something that is actually defined in the source.

Also added trivial test case.

[SVN r58416]

tools/bcp

@@ -1 +1 @@
-Subproject commit ee300ba7f62ac35ae106719293fe8cd3cd210305
+Subproject commit 7a5ebbfc865501953c16351100d10de0c21344a1