util/StringUtil: move comparison functions to StringCompare.cxx

src/playlist/plugins/ExtM3uPlaylistPlugin.cxx

@@ -25,6 +25,7 @@
 #include "tag/Tag.hxx"
 #include "tag/TagBuilder.hxx"
 #include "util/StringUtil.hxx"
+#include "util/StringCompare.hxx"
 #include "input/TextInputStream.hxx"
 
 #include <string.h>

src/playlist/plugins/SoundCloudPlaylistPlugin.cxx

@@ -24,7 +24,7 @@
 #include "config/Block.hxx"
 #include "input/InputStream.hxx"
 #include "tag/TagBuilder.hxx"
-#include "util/StringUtil.hxx"
+#include "util/StringCompare.hxx"
 #include "util/Alloc.hxx"
 #include "util/Error.hxx"
 #include "util/Domain.hxx"