cygwin*)
os_include_dir="os/newlib"
;;
+ darwin*)
+ # On Darwin, performance is improved if libstdc++ is single-module.
+ # Up to at least 10.3.5, -flat_namespace is required for proper
+ # treatment of coalesced symbols.
+ OPT_LDFLAGS="${OPT_LDFLAGS} -Wl,-single_module -Wl,-flat_namespace"
+ os_include_dir="os/generic"
+ ;;
*djgpp*) # leading * picks up "msdosdjgpp"
os_include_dir="os/djgpp"
;;