Use $CRT_DIR in more places.

Use $CRT_DIR in more places.

* configure.in (--with-crt-dir): Doc fix (now valid for all platforms).
(CRT_DIR): On (powerpc64|sparc64)-*-linux-gnu*, default to /usr/lib64.
On hpux10-20, default to /lib.

* src/m/amdx86-64.h (START_FILES, LIB_STANDARD): Change the logic around,
since the defaults (set by the system file) are fine in most cases.
[GNU_LINUX, __OpenBSD__, __NetBSD__, __APPLE__]: Remove sections.
* src/m/ibms390x.h (START_FILES, LIB_STANDARD):
* src/m/macppc.h (START_FILES, LIB_STANDARD) [GNU_LINUX]:
* src/m/sparc.h (START_FILES, LIB_STANDARD) [__linux__]:
Remove definitions, since they are set correctly in s/gnu-linux.h.
* src/s/freebsd.h (START_FILES, LIB_STANDARD):
* src/s/gnu-linux.h (START_FILES, LIB_STANDARD):
* src/s/hpux10-20.h (START_FILES):
* src/s/netbsd.h (START_FILES, LIB_STANDARD, START_FILES_1, END_FILES_1):
Use $CRT_DIR in place of fixed /usr/lib, /lib directories.

* src/Makefile.in: Comment.