collect2.c (main): Only generate import or export file and add to link arguments if non-empty.

        * collect2.c (main): Only generate import or export file and add
        to link arguments if non-empty.  Use xmalloc not alloca.
        (write_{export,import}_file): Delete.
        (write_aix_file): New function.
        (locatelib): Use xmalloc not malloc.
        (GCC_OK_SYMBOL): Do not check type if aix64.

From-SVN: r27106