linux-user: remove useless padding in flock64 structure

Since commit 8efb2ed5ec ("linux-user: Correct signedness of
target_flock l_start and l_len fields"), flock64 structure uses
abi_llong for l_start and l_len in place of "unsigned long long"
this should force them to be aligned accordingly to the target
rules. So we can remove the padding field and the QEMU_PACKED
attribute.

I have compared the result of the following program before and
after the change:

cat -> flock64_dump <<EOF
p/d sizeof(struct target_flock64)
p/d &((struct target_flock64 *)0)->l_type
p/d &((struct target_flock64 *)0)->l_whence
p/d &((struct target_flock64 *)0)->l_start
p/d &((struct target_flock64 *)0)->l_len
p/d &((struct target_flock64 *)0)->l_pid
quit
EOF

for file in build/all/*-linux-user/qemu-* ; do
echo $file
gdb -batch -nx -x flock64_dump $file 2> /dev/null
done

The sizeof() changes because we remove the QEMU_PACKED.
The new size is 32 (except for i386 and m68k) and this is
the real size of "struct flock64" on the target architecture.

The following architectures differ:
aarch64_be, aarch64, alpha, armeb, arm, cris, hppa, nios2, or1k,
riscv32, riscv64, s390x.

For a subset of these architectures, I have checked with the following
program the new structure is the correct one:

#include <stdio.h>
#define __USE_LARGEFILE64
#include <fcntl.h>

int main(void)
{
printf("struct flock64 %d\n", sizeof(struct flock64));
printf("l_type %d\n", &((struct flock64 *)0)->l_type);
printf("l_whence %d\n", &((struct flock64 *)0)->l_whence);
printf("l_start %d\n", &((struct flock64 *)0)->l_start);
printf("l_len %d\n", &((struct flock64 *)0)->l_len);
printf("l_pid %d\n", &((struct flock64 *)0)->l_pid);
}

[I have checked aarch64, alpha, hppa, s390x]

For ARM, the target_flock64 becomes the EABI definition, so we need to
define the OABI one in place of the EABI one and use it when it is
needed.

I have also fixed the alignment value for sh4 (to align llong on 4 bytes)
(see c2e3dee6e0 "linux-user: Define target alignment size")
[We should check alignment properties for cris, nios2 and or1k]

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180502215730.28162-1-laurent@vivier.eu>