bsd-user: Implement do_obreak function

bsd-user: Implement do_obreak function

Match linux-user, by manually applying the following commits, in order:

d28b3c90cfad1a7e211ae2bce36ecb9071086129   linux-user: Make sure initial brk(0) is page-aligned
15ad98536ad9410fb32ddf1ff09389b677643faa   linux-user: Fix qemu brk() to not zero bytes on current page
dfe49864afb06e7e452a4366051697bc4fcfc1a5   linux-user: Prohibit brk() to to shrink below initial heap address
eac78a4b0b7da4de2c0a297f4d528ca9cc6256a3   linux-user: Fix signed math overflow in brk() syscall
c6cc059eca18d9f6e4e26bb8b6d1135ddb35d81a   linux-user: Do not call get_errno() in do_brk()
e69e032d1a8ee8d754ca119009a3c2c997f8bb30   linux-user: Use MAP_FIXED_NOREPLACE for do_brk()
cb9d5d1fda0bc2312fc0c779b4ea1d7bf826f31f   linux-user: Do nothing if too small brk is specified
2aea137a425a87b930a33590177b04368fd7cc12   linux-user: Do not align brk with host page size

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230925182709.4834-19-kariem.taha2.7@gmail.com>