* configure.ac (opsysfile): Set to empty on freebsd, gnu-linux,
gnu-kfreebsd; and to usg5-4-common.h on sol2*, unixware.

* src/s/freebsd.h, src/s/gnu-linux.h, src/s/sol2-6.h, src/s/unixware.h:
Remove empty files.

* configure.ac (GC_SETJMP_WORKS, GC_MARK_STACK): Move here from src/s.
(AH_BOTTOM): Move GC_SETJMP_WORKS GCC fallback to main body.

* src/s/aix4-2.h, src/s/freebsd.h, src/s/gnu-linux.h, src/s/hpux10-20.h:
* src/s/irix6-5.h, src/s/netbsd.h, src/s/sol2-6.h, src/s/unixware.h:
Let configure set GC_SETJMP_WORKS, GC_MARK_STACK.

* configure.ac (opsysfile): Set to empty on gnu, cygwin.

* src/s/bsd-common, src/s/cygwin.h: Remove empty files.
* src/s/freebsd.h, src/s/netbsd.h: Do not include bsd-common.h.

* configure.ac (BSD4_2, BSD_SYSTEM, USG, USG5, _AIX, CYGWIN)
(DARWIN_OS, GNU_LINUX, HPUX, IRIX6_5, SOLARIS2):
Move "system type" macros here from src/s.
(BSD_SYSTEM_AHB): New hack macro.
(AH_BOTTOM): Set BSD_SYSTEM, using BSD_SYSTEM_AHB.

* src/s/usg5-4-common.h (USG, USG5):
* src/s/template.h (USG5, USG, HPUX, BSD4_2, BSD_SYSTEM):
* src/s/sol2-6.h (SOLARIS2):
* src/s/irix6-5.h (IRIX6_5):
* src/s/hpux10-20.h (USG, USG5, HPUX):
* src/s/gnu-linux.h (USG, GNU_LINUX):
* src/s/freebsd.h (BSD_SYSTEM):
* src/s/darwin.h (BSD4_2, BSD_SYSTEM, DARWIN_OS):
* src/s/cygwin.h (CYGWIN):
* src/s/bsd-common.h (BSD_SYSTEM, BSD4_2):
* src/s/aix4-2.h (USG, USG5, _AIX): Move "system type" macros to configure.

* configure.ac (BROKEN_GET_CURRENT_DIR_NAME, BROKEN_PTY_READ_AFTER_EAGAIN)
(G_SLICE_ALWAYS_MALLOC): Move here from src/s.

* src/s/freebsd.h (BROKEN_PTY_READ_AFTER_EAGAIN):
* src/s/cygwin.h (G_SLICE_ALWAYS_MALLOC):
* src/s/aix4-2.h (BROKEN_GET_CURRENT_DIR_NAME): Let configure set them.

* configure.ac (DONT_REOPEN_PTY): Move here from src/s.

* src/s/darwin.h, src/s/freebsd.h, src/s/netbsd.h:
Move DONT_REOPEN_PTY to configure.

* configure.ac (PENDING_OUTPUT_COUNT): Move here from src/s.

* src/s/cygwin.h, src/s/darwin.h, src/s/freebsd.h, src/s/netbsd.h:
* src/s/unixware.h: Move PENDING_OUTPUT_COUNT definition to configure.

* lisp.h (GC_MARK_STACK): Default to GC_MAKE_GCPROS_NOOPS.
* s/cygwin.h, s/darwin.h, s/freebsd.h, s/gnu.h, s/irix6-5.h, s/msdos.h:
* s/netbsd.h, s/sol2-6.h:
Remove definition of GC_MARK_STACK, since the default now works.
* s/aix4-2.h, s/hpux10-20.h, s/unixware.h:
Define GC_MARK_STACK to GC_USE_GCPROS_AS_BEFORE, since that's
no longer the default.
* s/gnu-linux.h (GC_MARK_STACK): Adjust to change in default.