Fix configure .pc files generation and make install when

--build-suffix is used.

Patch by Anatoly Nenashev ${surname}_as@mail.ru.

Originally committed as revision 24821 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -3217,7 +3217,7 @@ comment=$2
 version=$3
 libs=$4
 requires=$5
-enabled $shortname || return 0
+enabled ${name#lib} || return 0
 cat <<EOF > $name/$name.pc
 prefix=$prefix
 exec_prefix=\${prefix}