build: Add missing config.sh dependency for pkg-config files

Also only update config.sh when it changed to avoid spurious rebuilds.

configure

@@ -5385,7 +5385,7 @@ print_enabled_components libavformat/protocol_list.c URLProtocol url_protocols $
 
 # Settings for pkg-config files
 
-cat > avbuild/config.sh <<EOF
+cat > $TMPH <<EOF
 # Automatically generated by configure - do not modify!
 shared=$shared
 prefix=$prefix
@@ -5407,3 +5407,5 @@ for lib in $LIBRARY_LIST; do
     lib_deps="$(eval echo \$${lib}_deps)"
     echo ${lib}_deps=\"$lib_deps\" >> avbuild/config.sh
 done
+
+cp_if_changed $TMPH avbuild/config.sh