#13 Fix a -pthread build issue for Ubuntu Linux

[chasm!killer]

To build from the current top of tree I had to patch the Makefile after running ./configure to add the -pthread flag to the gc++ command macro for compiling and linking.

The hacks I put into the two files aclocal.m4 and configure.ac are definitely not what should go into a permanent archive, but they do seem to do the right thing. I did not know how to implement the substitution of the acx_pthread values for the non-pthread ones as described in

http://autoconf-archive.cryp.to/acx_pthread.html

so I just hacked them inline in the macro and copied it to the aclocal.m4 file. And the change to configure.ac is just to call the hacked acx_pthread macro.

I also had a second problem with using sysctl() to get the number of processors (the Debian gc++ distributed as part of the Ubuntu distribution does not support the sysctl() method, but rather a sysconf() method. Since it is completely unrelated to this patch, I'm submitting it as a second patch.

[chasm!killer]

unified diff for the patch