Use proper linker command for drivers on OpenBSD

This fixes the "Cannot load specified object" / setuid_drv.so: undefined symbol '__guard_local' error that occurs on OpenBSD 5.3. It changes the LD_SHARED variable to use gcc rather than ld. A similar issue is documented here: http://erlang.org/pipermail/erlang-questions/2013-May/073837.html. Tested on OpenBSD 5.3 and FreeBSD 9.
Merge pull request #151 from fjoanis/master

Fix runtime error on OpenBSD 5.3
Try to make the log directory if it doesn't exist

This uses @capflam's patch from https://github.com/klacke/yaws/pull/145
to create the log directory if specified like

    logdir = +path/to/log

in the configuration file.
Merge remote-tracking branch 'MrStaticVoid/yaws-1.96/try-to-create...

...-log-dir-if-specified-in-config'