Bump bundled libarchive version to 3.5.2

- Update bunlded libarchive version used on Windows/Mac
- Enable requested zstd support while we are at it. Closes #211

dependencies/libarchive-3.5.2/build/cmake/CreatePkgConfigFile.cmake

@@ -0,0 +1,33 @@
+# - Generate a libarchive.pc like autotools for pkg-config
+#
+
+# Set the required variables (we use the same input file as autotools)
+SET(prefix ${CMAKE_INSTALL_PREFIX})
+SET(exec_prefix \${prefix})
+SET(libdir \${exec_prefix}/lib)
+SET(includedir \${prefix}/include)
+# Now, this is not particularly pretty, nor is it terribly accurate...
+# Loop over all our additional libs
+FOREACH(mylib ${ADDITIONAL_LIBS})
+	# Extract the filename from the absolute path
+	GET_FILENAME_COMPONENT(mylib_name ${mylib} NAME_WE)
+	# Strip the lib prefix
+	STRING(REGEX REPLACE "^lib" "" mylib_name ${mylib_name})
+	# Append it to our LIBS string
+	SET(LIBS "${LIBS} -l${mylib_name}")
+ENDFOREACH()
+# libxml2 is easier, since it's already using pkg-config
+FOREACH(mylib ${PC_LIBXML_STATIC_LDFLAGS})
+	SET(LIBS "${LIBS} ${mylib}")
+ENDFOREACH()
+# FIXME: The order of the libraries doesn't take dependencies into account,
+#	 thus there's a good chance it'll make some binutils versions unhappy...
+#	 This only affects Libs.private (looked up for static builds) though.
+CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/build/pkgconfig/libarchive.pc.in
+		${CMAKE_CURRENT_BINARY_DIR}/build/pkgconfig/libarchive.pc
+		@ONLY)
+# And install it, of course ;).
+IF(ENABLE_INSTALL)
+  INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/build/pkgconfig/libarchive.pc
+          DESTINATION "lib/pkgconfig")
+ENDIF()