sysutils/nut-devel: Remove GCC requirement.

Remove the GCC requirement by adding -lpthread and removing the
nullification of CFLAGS and LDFLAGS in the M4 script that verifies
we have a working libltdl.

sysutils/nut-devel/Makefile

@@ -22,7 +22,6 @@ GH_TAGNAME=	2ced48d1b
 NUT_COMMIT_DATE=	2023.07.30
 
 MAKE_JOBS_UNSAFE=	yes
-USE_GCC=	yes
 GNU_CONFIGURE=	yes
 USES=		autoreconf:build compiler:c11 gmake libtool pkgconfig python
 USE_LDCONFIG=	yes
@@ -84,7 +83,7 @@ CONFIGURE_ARGS=	--sysconfdir=${PREFIX}/etc/nut \
 		--with-dev \
 		--with-ltdl --with-nut-scanner
 
-CFLAGS+=	-I${LOCALBASE}/include -L${LOCALBASE}/lib
+CFLAGS+=	-I${LOCALBASE}/include -L${LOCALBASE}/lib -lpthread
 LIB_DEPENDS+=	libltdl.so:devel/libltdl
 
 # XXX Remove this when copying this port to sysutils/nut. The GA version

sysutils/nut-devel/files/patch-m4_nut__check_libltdl.m4

@@ -0,0 +1,21 @@
+--- m4/nut_check_libltdl.m4.orig	2023-08-01 07:33:24.593954000 -0700
++++ m4/nut_check_libltdl.m4	2023-08-01 07:35:18.506094000 -0700
+@@ -10,10 +10,7 @@
+ 	dnl No NUT_CHECK_PKGCONFIG here: (lib)ltdl.pc was not seen on any OS
+
+ 	dnl save CFLAGS and LIBS
+-	CFLAGS_ORIG="${CFLAGS}"
+-	LIBS_ORIG="${LIBS}"
+ 	LIBS=""
+-	CFLAGS=""
+ 	dnl For fallback below:
+ 	myCFLAGS=""
+
+@@ -71,7 +68,5 @@
+ 	unset myCFLAGS
+
+ 	dnl restore original CFLAGS and LIBS
+-	CFLAGS="${CFLAGS_ORIG}"
+-	LIBS="${LIBS_ORIG}"
+ fi
+ ])