Remove some cpp that is internal to configure.in.

Remove some cpp that is internal to configure.in.

* configure.in (C_OPTIMIZE_SWITCH, CANNOT_DUMP, SYSTEM_MALLOC):
(USE_MMAP_FOR_BUFFERS, C_WARNING_SWITCH): Set with shell, not cpp.
(LIBX): Remove, just use -lX11 in the one place this was used.
(cannot_dump): Replace with CANNOT_DUMP.

* src/Makefile.in (CANNOT_DUMP): Update for configure name change.

* src/s/freebsd.h (USE_MMAP_FOR_BUFFERS):
* src/s/irix6-5.h (USE_MMAP_FOR_BUFFERS):
* src/s/darwin.h (SYSTEM_MALLOC):
* src/s/sol2-10.h (SYSTEM_MALLOC): Move to configure.

* src/m/alpha.h: Remove old comment.
* src/s/aix4-2.h: Update comment.
* src/s/template.h: Remove USE_MMAP_FOR_BUFFERS.

* msdos/sed1v2.inp (CANNOT_DUMP): Update for configure name change.

* admin/CPP-DEFINES: Remove USE_MMAP_FOR_BUFFERS, CANNOT_DUMP.

* etc/DEBUG: Update SYSTEM_MALLOC and CANNOT_DUMP references.
Some re-filling.