place.

This moves the dependency on GCC's and other compiler's features into
the central sys/cdefs.h file, while the individual source files can
then refer to #ifdef __COMPILER_FEATURE_FOO where they by now used to
refer to #if __GNUC__ > 3.1415 && __BARC__ <= 42.

By now, GCC and ICC (the Intel compiler) have been actively tested on
IA32 platforms by netchild.  Extension to other compilers is supposed
to be possible, of course.

Submitted by:	netchild
Reviewed by:	various developers on arch@, some time ago

to build the kernel. It doesn't affect the operation if gcc.

Most of the changes are just adding __INTEL_COMPILER to #ifdef's, as
icc v8 may define __GNUC__ some parts may look strange but are
necessary.

Additional changes:
 - in_cksum.[ch]:
   * use a generic C version instead of the assembly version in the !gcc
     case (ASM code breaks with the optimizations icc does)
     -> no bad checksums with an icc compiled kernel
     Help from:		andre, grehan, das
     Stolen from: 	alpha version via ppc version
     The entire checksum code should IMHO be replaced with the DragonFly
     version (because it isn't guaranteed future revisions of gcc will
     include similar optimizations) as in:
        ---snip---
          Revision  Changes    Path
          1.12      +1 -0      src/sys/conf/files.i386
          1.4       +142 -558  src/sys/i386/i386/in_cksum.c
          1.5       +33 -69    src/sys/i386/include/in_cksum.h
          1.5       +2 -0      src/sys/netinet/igmp.c
          1.6       +0 -1      src/sys/netinet/in.h
          1.6       +2 -0      src/sys/netinet/ip_icmp.c

          1.4       +3 -4      src/contrib/ipfilter/ip_compat.h
          1.3       +1 -2      src/sbin/natd/icmp.c
          1.4       +0 -1      src/sbin/natd/natd.c
          1.48      +1 -0      src/sys/conf/files
          1.2       +0 -1      src/sys/conf/files.amd64
          1.13      +0 -1      src/sys/conf/files.i386
          1.5       +0 -1      src/sys/conf/files.pc98
          1.7       +1 -1      src/sys/contrib/ipfilter/netinet/fil.c
          1.10      +2 -3      src/sys/contrib/ipfilter/netinet/ip_compat.h
          1.10      +1 -1      src/sys/contrib/ipfilter/netinet/ip_fil.c
          1.7       +1 -1      src/sys/dev/netif/txp/if_txp.c
          1.7       +1 -1      src/sys/net/ip_mroute/ip_mroute.c
          1.7       +1 -2      src/sys/net/ipfw/ip_fw2.c
          1.6       +1 -2      src/sys/netinet/igmp.c
          1.4       +158 -116  src/sys/netinet/in_cksum.c
          1.6       +1 -1      src/sys/netinet/ip_gre.c
          1.7       +1 -2      src/sys/netinet/ip_icmp.c
          1.10      +1 -1      src/sys/netinet/ip_input.c
          1.10      +1 -2      src/sys/netinet/ip_output.c
          1.13      +1 -2      src/sys/netinet/tcp_input.c
          1.9       +1 -2      src/sys/netinet/tcp_output.c
          1.10      +1 -1      src/sys/netinet/tcp_subr.c
          1.10      +1 -1      src/sys/netinet/tcp_syncache.c
          1.9       +1 -2      src/sys/netinet/udp_usrreq.c

          1.5       +1 -2      src/sys/netinet6/ipsec.c
          1.5       +1 -2      src/sys/netproto/ipsec/ipsec.c
          1.5       +1 -1      src/sys/netproto/ipsec/ipsec_input.c
          1.4       +1 -2      src/sys/netproto/ipsec/ipsec_output.c

          and finally remove
            sys/i386/i386        in_cksum.c
            sys/i386/include     in_cksum.h
        ---snip---
 - endian.h:
   * DTRT in C++ mode
 - quad.h:
   * we don't use gcc v1 anymore, remove support for it
   Suggested by:	bde (long ago)
 - assym.h:
   * avoid zero-length arrays (remove dependency on a gcc specific
     feature)
     This change changes the contents of the object file, but as it's
     only used to generate some values for a header, and the generator
     knows how to handle this, there's no impact in the gcc case.
   Explained by:	bde
   Submitted by:	Marius Strobl <marius@alchemy.franken.de>
 - aicasm.c:
   * minor change to teach it about the way icc spells "-nostdinc"
   Not approved by:	gibbs (no reply to my mail)
 - bump __FreeBSD_version (lang/icc needs to know about the changes)

Incarnations of this patch survive gcc compiles since a loooong time,
I use it on my desktop. An icc compiled kernel works since Nov. 2003
(exceptions: snd_* if used as modules), it survives a build of the
entire ports collection with icc.

Parts of this commit contains suggestions or submissions from
Marius Strobl <marius@alchemy.franken.de>.

Reviewed by:	-arch
Submitted by:	netchild

ready for it yet.

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore.  This update would have been
insane otherwise.

Exchange control<->addr_type fields

Obtained from: NetBSD

and my own ideas