MFC r210431:

MFC r210431:
Remove the linux_exec_copyin_args(), freebsd32_exec_copyin_args() may
serve as well. COMPAT_FREEBSD32 is a prerequisite for COMPAT_LINUX32.

MFC r210451:
Use forward declartion for enum uio_seg in imgact.h. This allows to remove
inclusion of sys/uio.h from the header.

MFC r210498:
Revert r210451, and the similar part of the r210431. The forward-declaration
for the enum tag when enum definition is not complete is not allowed by
C99, and is gcc extension.

MFC r210501:
Remove unneeded includes.

Requested by:	dchagin

git-svn-id: svn://svn.freebsd.org/base/stable/8@219155 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f