Add -Wno-multichar to WARNINGS_C*FLAGS for BeOS. Thanks to "Yannick Koehler" <koehler@mythrium.com> for the patch.

configure.in

@@ -506,6 +506,8 @@ case "$target" in
     MKSHLIB='$(CXX) $(DSO_LDOPTS)'
     DSO_LDOPTS='-nostart -Xlinker --ignore-undefined'
     TK_LIBS='-lbe -lroot'
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wno-multichar"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-multichar"
     ;;
 
 *-bsdi*)