devel/libarchive: Drop Requires.private field from pkgconfig file.

Some failures will otherwise result in dependent ports since we do
not have a pkg-config file for iconv.
Reported and analyzed by sthen@

archivers/libarchive/Makefile

@@ -1,6 +1,7 @@
 COMMENT=	multi-format archive and compression library
 
 DISTNAME=	libarchive-3.6.2
+REVISION=	0
 SHARED_LIBS=	archive		13.0	# 19.2
 CATEGORIES=	archivers
 HOMEPAGE=	https://www.libarchive.org/

archivers/libarchive/patches/patch-build_pkgconfig_libarchive_pc_in

@@ -0,0 +1,12 @@
+Drop Requires.private field from pkgconfig file.  Some failures
+will otherwise result in dependent ports since we do not have a
+pkg-config file for iconv.
+
+Index: build/pkgconfig/libarchive.pc.in
+--- build/pkgconfig/libarchive.pc.in.orig
++++ build/pkgconfig/libarchive.pc.in
+@@ -10,4 +10,3 @@ Cflags: -I${includedir}
+ Cflags.private: -DLIBARCHIVE_STATIC
+ Libs: -L${libdir} -larchive
+ Libs.private: @LIBS@
+-Requires.private: @LIBSREQUIRED@