Port to Solaris 10 sparc + Sun C 5.13

Port to Solaris 10 sparc + Sun C 5.13

* configure.ac (SETUP_SLAVE_PTY) [sol2* | unixware]:
Adjust to process.c change.
* src/process.c (create_process): Declare volatile variables at
top level of this function, so that they're less likely to be
reused later in the function in the code executed by the vforked
child.  Do not declare locals used only in the vforked child, as
they might share memory with locals still live in the parent.
Instead, use the same variables in the child as in the parent.
This works around a subtle bug that causes a garbage collector
crash when Emacs is built with Sun C 5.13 sparc on Solaris 10.