No longer install sys/nv.h and sys/cnv.h in lib/libnv/Makefile

Use tools/build/Makefile to install the headers into ${WORLDTMP}/legacy
instead. Compared to r336026 this has the minor advantage that it avoids
unncessary header installation when building the non-bootstrap libnv.

Reviewed By:	bdrewery, kevans
Approved By:	brooks (mentor)
Differential Revision: https://reviews.freebsd.org/D16187

lib/libnv/Makefile

@@ -17,9 +17,6 @@ SRCS+=	msgio.c
 SRCS+=	nvlist.c
 SRCS+=	nvpair.c
 
-INCSDIR=	${INCLUDEDIR}/sys
-INCS=	${SRCTOP}/sys/sys/cnv.h ${SRCTOP}/sys/sys/nv.h
-
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
 

tools/build/Makefile

@@ -49,4 +49,7 @@ SRCS=		dummy.c
 SUBDIR=		cross-build
 .endif
 
+# Needed to build config (since it uses libnv)
+SYSINCS+=	${SRCTOP}/sys/sys/nv.h ${SRCTOP}/sys/sys/cnv.h
+
 .include <bsd.lib.mk>