Remove MINIXSRCDIR and use NETBSDSRCDIR

NETBSDSRCDIR is used all over the place anyway, and this reduces
our diff with NetBSD a little.

include/arch/i386/include/Makefile.inc

@@ -1,5 +1,5 @@
 .include <bsd.own.mk>
-.PATH: ${MINIXSRCDIR}/common/include/arch/i386
+.PATH: ${NETBSDSRCDIR}/common/include/arch/i386
 
 INCS+=	archtypes.h bios.h cmos.h cpu.h diskparm.h fpu.h int86.h \
 	interrupt.h memory.h multiboot.h partition.h \

include/minix/Makefile

@@ -6,7 +6,7 @@ INCSDIR=	/usr/include/minix
 
 INCS+= dirent.h paths.h types.h
 
-.include "${MINIXSRCDIR}/common/include/sys/Makefile.mount.inc"
-.include "${MINIXSRCDIR}/common/include/Makefile.termios.inc"
+.include "${NETBSDSRCDIR}/common/include/sys/Makefile.mount.inc"
+.include "${NETBSDSRCDIR}/common/include/Makefile.termios.inc"
 
 .include <bsd.kinc.mk>

include/sys/Makefile

@@ -55,7 +55,7 @@ namei: namei.src gennameih.awk
 	${TOOL_AWK} -f gennameih.awk < namei.src
 
 .include <bsd.own.mk>
-.include "${MINIXSRCDIR}/common/include/sys/Makefile.inc"
+.include "${NETBSDSRCDIR}/common/include/sys/Makefile.inc"
 
 .include <bsd.files.mk>
 .include <bsd.kinc.mk>