Work around deprecated TagLib::String::null

PKGBUILD

@@ -35,6 +35,9 @@ build() {
   # http://site.icu-project.org/download/61#TOC-Migration-Issues
   export CPPFLAGS+=' -DU_USING_ICU_NAMESPACE=1'
 
+  # Work around deprecated TagLib::String::null from TagLib 1.12
+  CXXFLAGS+=' -Wno-error=deprecated-declarations'
+
   BOOST_LIB_SUFFIX='' ./configure \
     --prefix=/usr \
     --enable-clock \