tmpnam() usage replaced with mkstemp(). Find a suitable tmp directory
checking the TMPDIR environment variable first, then the P_tmpdir
macro and finally /tmp directly.
On 64-bit Linux platforms, check to see if libc.so exists in /usr/lib64.
If found, use it over /usr/lib/libc.so.
The libc.so file is not always in /usr/lib. On multilib systems, the
file we care about could be in /usr/lib64. Likewise, common Linux
conventions call for 64-bit libraries to go in lib64 directories, so
check there first when on a Linux 64-bit system.
