Make libohash a proper internallib instead of hidding it in m4

mandoc development seems to be also using ohash so prepare to share the code when
needed

lib/Makefile

@@ -69,6 +69,7 @@ SUBDIR=	${SUBDIR_ORDERED} \
 	${_libnetgraph} \
 	${_libngatm} \
 	libnv \
+	libohash \
 	libopie \
 	libpam \
 	libpcap \

lib/libohash/Makefile

@@ -0,0 +1,9 @@
+# $FreeBSD$
+
+LIB=	ohash
+SRCS=	ohash.c
+INTERNALLIB=
+
+WARNS=	3
+
+.include <bsd.lib.mk>

share/mk/src.libnames.mk

@@ -44,3 +44,7 @@ LIBUCL?=	${LIBUCLDIR}/libucl.a
 LIBREADLINEDIR=	${ROOTOBJDIR}/gnu/lib/libreadline/readline
 LDREADLINE?=	${LIBREADLINEDIR}/libreadline.a
 LIBREADLINE?=	${LIBREADLINEDIR}/libreadline.a
+
+LIBOHASHDIR=	${ROOTOBJDIR}/lib/libohash
+LDOHASH?=	${LIBOHASHDIR}/libohash.a
+LIBOHASH?=	${LIBOHASHDIR}/libohash.a

usr.bin/m4/Makefile

@@ -7,16 +7,13 @@
 .include <src.opts.mk>
 
 PROG=	m4
-CFLAGS+=-DEXTENDED -I${.CURDIR} -I${.CURDIR}/lib
-DPADD=	${LIBY} ${LIBL} ${LIBM}
-LDADD=	-ly -ll -lm
+CFLAGS+=-DEXTENDED -I${.CURDIR} -I${.CURDIR}/../../lib/libohash
+DPADD=	${LIBY} ${LIBL} ${LIBM} ${LIBOHASH}
+LDADD=	-ly -ll -lm ${LDOHASH}
 
 NO_WMISSING_VARIABLE_DECLARATIONS=
 
 SRCS=	eval.c expr.c look.c main.c misc.c gnum4.c trace.c parser.y tokenizer.l
-.PATH: ${.CURDIR}/lib
-SRCS+=	ohash.c
-WARNS=	3
 
 tokenizer.o: parser.h