osslsigncode: fixed build error against system openssl

Tested on two different machines on Mac OS X 10.8 with the latest `brew update`, `osslsigncode` fails to build with this error:

```
==> Downloading http://downloads.sourceforge.net/project/osslsigncode/osslsigncode/osslsigncode-1.5.2.tar.gz
Already downloaded: /Library/Caches/Homebrew/osslsigncode-1.5.2.tar.gz
==> ./configure --prefix=/usr/local/Cellar/osslsigncode/1.5.2
==> make install
  "_ERR_remove_thread_state", referenced from:
      _cleanup_lib_state in osslsigncode.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [osslsigncode] Error 1
```

According to a search on Google this is because OpenSSL's `ERR_remove_thread_state` was not introduced until version 1.0. The Apple system OpenSSL is 0.9.8 so we need to depend on the newer brew version instead.

With this patch `osslsigncode` builds correctly and the resulting binary works fine.