libarchive: Quote all sed commands in fake-libarchive-pc target

At least the last `-e' contains whitespaces and can be problematic.
Avoid that by quoting all commands.

Should fix PR pkg/53347.

Index: builtin.mk
===================================================================
RCS file: /cvsroot/pkgsrc/archivers/libarchive/builtin.mk,v
retrieving revision 1.7
diff -u -p -r1.7 builtin.mk
--- builtin.mk	6 Jun 2018 14:21:09 -0000	1.7
+++ builtin.mk	7 Jun 2018 10:53:20 -0000
@@ -113,12 +113,12 @@ fake-libarchive-pc:
 			${LN} -sf $${src} $${dst};					\
 		else									\
 			${ECHO_BUILDLINK_MSG} "Creating $${dst}";			\
-			${SED}  -e s,@prefix@,${BUILDLINK_PREFIX.libarchive},		\
-					-e s,@exec_prefix@,${BUILDLINK_PREFIX.libarchive},\
-					-e s,@libdir@,${BUILDLINK_PREFIX.libarchive}/lib${LIBABISUFFIX},\
-					-e s,@includedir@,${BUILDLINK_PREFIX.libarchive}/include,\
-					-e s,@VERSION@,${BUILTIN_VERSION.libarchive},	\
-					-e s,@LIBS@,-llzma -lbz2 -lz,			\
+			${SED}  -e 's,@prefix@,${BUILDLINK_PREFIX.libarchive},'		\
+					-e 's,@exec_prefix@,${BUILDLINK_PREFIX.libarchive},'\
+					-e 's,@libdir@,${BUILDLINK_PREFIX.libarchive}/lib${LIBABISUFFIX},'\
+					-e 's,@includedir@,${BUILDLINK_PREFIX.libarchive}/include,'\
+					-e 's,@VERSION@,${BUILTIN_VERSION.libarchive},' \
+					-e 's,@LIBS@,-llzma -lbz2 -lz,'			\
 				$${sedsrc} > $${dst};					\
 		fi									\
 	fi