Consolidate strerror handling, as well as getcwd/getwd.

Consolidate strerror handling, as well as getcwd/getwd.

        * configure.in (GCC_NEED_DECLARATIONS): Add strerror, getcwd and
        getwd.
        * acconfig.m4: Add stubs for NEED_DECLARATION_STRERROR,
        NEED_DECLARATION_GETCWD and NEED_DECLARATION_GETWD.
        * cccp.c: Remove strerror()/sys_nerr/sys_errlist decls.
        (my_strerror): Add prototype and make it static.
        * collect2.c: Likewise.
        * cpplib.c: Likewise.
        * gcc.c: Likewise, but keep `my_strerror' extern.
        * protoize.c: Likewise.
        * pexecute.c (my_strerror): Add argument to prototype.
        * system.h: Add prototypes for getcwd, getwd and strerror.  Add
        extern decls for sys_nerr and sys_errlist.  Make abort decl
        explicitly extern.
        * getpwd.c: Remove decls for getwd and getcwd.

From-SVN: r20779