Never hardcode /sys into these Makefiles. The proper way to spell it is $S.

Also, move the -I stuff to the centralized kern.pre.mk.  However, it
might be better to add these flags to files.conf.  This is a short
term fix to fix the broken builds on my machine (I don't have a valid
/sys link).

sys/conf/Makefile.alpha

@@ -87,6 +87,4 @@ __reml.S: $S/$M/$M/divrem.m4
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.amd64

@@ -52,6 +52,4 @@ MKMODULESENV+= MACHINE=amd64
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.arm

@@ -58,6 +58,4 @@ ldscript.$M: $S/conf/ldscript.$M
 	  sed s/KERNVIRTADDR/${KERNVIRTADDR}/g > ldscript.$M
 %RULES
 	
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.i386

@@ -46,6 +46,4 @@ MKMODULESENV+= MACHINE=i386
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.ia64

@@ -52,6 +52,4 @@ ASM_CFLAGS= -x assembler-with-cpp -Wa,-x -DLOCORE ${CFLAGS}
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.pc98

@@ -46,6 +46,4 @@ MKMODULESENV+=	MACHINE=pc98
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.powerpc

@@ -51,6 +51,4 @@ CFLAGS+=	-fno-omit-frame-pointer
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/Makefile.sparc64

@@ -46,6 +46,4 @@ MDOBJS=	exception.o interrupt.o
 
 %RULES
 
-CFLAGS+=-I/sys/dev/twa
-
 .include "$S/conf/kern.post.mk"

sys/conf/kern.pre.mk

@@ -67,6 +67,9 @@ INCLUDES+= -I$S/contrib/dev/ath -I$S/contrib/dev/ath/freebsd
 # ... and the same for the NgATM stuff
 INCLUDES+= -I$S/contrib/ngatm
 
+# .. and the same for twa
+INCLUDES+= -I$S/dev/twa
+
 CFLAGS=	${COPTFLAGS} ${CWARNFLAGS} ${DEBUG}
 CFLAGS+= ${INCLUDES} -D_KERNEL -include opt_global.h
 .if ${CC} != "icc"