Reduce compiler/libraries/headers cases to only two

1. ack, a.out, minix headers (moved to /usr/include.ack),
	   minix libc
	2. gcc/clang, elf, netbsd headers (moved to /usr/include),
	   netbsd libc (moved to /usr/lib)

So this obsoletes the /usr/netbsd hierarchy.

No special invocation for netbsd libc necessary - it's always used
for gcc/clang.

nbsd_include/arch/Makefile

@@ -53,10 +53,10 @@ SUBDIR+= xen
 #	x68k x86_64 xen \
 #	zaurus
 
-INCSYMLINKS= ${MACHINE} /usr/netbsd/include/machine
+INCSYMLINKS= ${MACHINE} /usr/include/machine
 
-INCSYMLINKS+= machine/float.h /usr/netbsd/include/float.h \
-       machine/stdarg.h /usr/netbsd/include/stdarg.h
+INCSYMLINKS+= machine/float.h /usr/include/float.h \
+       machine/stdarg.h /usr/include/stdarg.h
 
 
 .include <bsd.inc.mk>

nbsd_include/arch/i386/include/Makefile

@@ -1,7 +1,7 @@
 #	$NetBSD: Makefile,v 1.36 2007/12/20 23:46:12 ad Exp $
 .include <bsd.own.mk>
 
-INCSDIR= /usr/netbsd/include/i386
+INCSDIR= /usr/include/i386
 
 INCS= 	ansi.h asm.h bswap.h byte_swap.h cdefs.h \
 	endian.h endian_machdep.h fenv.h float.h ieee.h \

nbsd_include/arch/x86/include/Makefile

@@ -1,6 +1,6 @@
 # 	$NetBSD: Makefile,v 1.13 2008/05/11 15:32:20 ad Exp $
 
-INCSDIR=/usr/netbsd/include/x86
+INCSDIR=/usr/include/x86
 
 INCS=	float.h \
 	ieee.h \