Replace AT_EXECFN in auxiliary vectors of programs executed on Android

Replace AT_EXECFN in auxiliary vectors of programs executed on Android

* exec/exec.c (insert_args, exec_0): On non-MIPS systems, copy
NAME and its length to the loader area.  State that MIPS support
is not yet available (though it will be pending the availability
of a functioning emulator).

* exec/loader-aarch64.s (_start):

* exec/loader-armeabi.s (_start):

* exec/loader-x86.s (_start):

* exec/loader-x86_64.s (_start): Displace auxv, environ, and
argv to create sufficient space for the provided file name, and
copy the file name there.  Replace AT_EXECFN to refer to this
space.

(cherry picked from commit 7a01350624e1665e707f98e13d51f53e9f87ce95)