(gl_SYS__SYSTEM_CONFIGURATION): New macro.

(gl_SYS__SYSTEM_CONFIGURATION): New macro.
(gl_PHYSMEM): Use it.
Also check for `table' function.
Check for new headers and functions.
Add check for sys/sysmp.h.
With suggestions from Kaveh Ghazi.
Ignore headers that are present but cannot be compiled.  This
avoids spurious warnings on Solaris 9 sparc with Forte Developer 7
C 5.4.