linux-user: Properly Handle semun Structure In Cross-Endian Situations

linux-user: Properly Handle semun Structure In Cross-Endian Situations

The semun union used in the semctl system call contains both an int (val) and
pointers.  In cross-endian situations on 64 bit targets, the value passed to
semctl is an 8 byte (abi_long) value and thus does not have the 4-byte val
field in the correct location.  In order to rectify this, the other half
of the union must be accessed.  This is achieved in code by performing
a byte swap on the entire 8 byte union, followed by a 4-byte swap of the
first half.

Also, eliminate an extraneous (dead) line of code that sets target_su.val in
the IPC_SET/IPC_GET case.

Signed-off-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>