[gdbserver] disable Elf32_auxv_t/Elf64_auxv_t AC_CHECK_TYPES check on Android

See the comment added in configure.ac for more details behind
this change.

gdb/gdbserver/ChangeLog:

        * configure.ac: Do not call AC_CHECK_TYPES for Elf32_auxv_t
        and Elf64_auxv_t if the target is Android.