Define LIB_STANDARD and START_FILES using autoconf.

Define LIB_STANDARD and START_FILES using autoconf.
* s/usg5-4.h (LIB_STANDARD):
* s/netbsd.h (START_FILES):
* s/irix6-5.h (LIB_STANDARD):
* s/hpux10-20.h (LIB_STANDARD, START_FILES):
* s/gnu-linux.h (START_FILES, LIB_STANDARD):
* s/freebsd.h (START_FILES):
* s/darwin.h (START_FILES):
* s/cygwin.h (START_FILES):
* s/aix4-2.h (LIB_STANDARD):
* m/ibmrs6000.h (START_FILES): Remove, move logic to configure.in.
* Makefile.in (STARTFILES): Rename to START_FILES, define using
autoconf, not cpp.

Define START_FILES and LIB_STANDARD using autoconf.
* configure.in (START_FILES, LIB_STANDARD): New definitions, moved
here from src/s/*.h.
(HAVE_CRTIN): Remove, inline logic in the netbsd
START_FILES/LIB_STANDARD computation.