Explicitly set C98 for this target

Sometime I'd like to get the lib over to C++1x, but for now, enforce
the currently in-use standard.

taglib/CMakeLists.txt

@@ -337,6 +337,7 @@ set(tag_LIB_SRCS
 )
 
 add_library(tag ${tag_LIB_SRCS} ${tag_HDRS})
+set_property(TARGET tag PROPERTY CXX_STANDARD 98)
 
 if(HAVE_ZLIB AND NOT HAVE_ZLIB_SOURCE)
   target_link_libraries(tag ${ZLIB_LIBRARIES})