Provide <sys/user.h>.

strace wants this, for example.

Change-Id: Icb4d64bde392abbc091fa3375a4fa19b2707b12c
libc: krait: Use performance version of bcopy and memmove

Ported from CM10.2.

bionic-benchmarks on mako:
before:
                     iterations      ns/op
BM_string_memmove/8    50000000         32   243.54 MiB/s
BM_string_memmove/64   20000000        143   446.41 MiB/s
BM_string_memmove/512    2000000        885   578.14 MiB/s
BM_string_memmove/1K    1000000       1733   590.55 MiB/s
BM_string_memmove/8K     200000      13618   601.54 MiB/s
BM_string_memmove/16K     100000      27276   600.66 MiB/s
BM_string_memmove/32K      50000      59115   554.30 MiB/s
BM_string_memmove/64K      10000     118162   554.63 MiB/s

after:
                     iterations      ns/op
BM_string_memmove/8    50000000         20   381.94 MiB/s
BM_string_memmove/64  100000000         17  3636.07 MiB/s
BM_string_memmove/512   50000000         50 10116.80 MiB/s
BM_string_memmove/1K   20000000         98 10429.23 MiB/s
BM_string_memmove/8K    2000000        876  9346.43 MiB/s
BM_string_memmove/16K    1000000       1836  8923.09 MiB/s
BM_string_memmove/32K     500000       4392  7459.79 MiB/s
BM_string_memmove/64K     200000       8562  7653.85 MiB/s

Change-Id: Id64913a71857d9cfdf6bd1bbe2c66cfc49d72748