https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64023
--- Comment #2 from Iain Sandoe <iains at gcc dot gnu.org> --- as commented in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63773 c#14..17 this is caused by $(HOST_EXPORTS) being used at stage#N>1 instead of $(POSTSTAGE1_HOST_EXPORTS) Thus the config test for the bootstrap compiler is affecting the later build. In this case, GCC fails to build because it supports -static-libstdc++ (and thus the option is passed to the build) but it then needs the -B options to allow for spec substitution to work for libstdc++. These are not present in HOST_EXPORTS because, obviously, the host compiler is installed and doesn't need them. NOTE: (clang succeeds because it does not support -staticlibstdc++, so that option is not passed to the stage#3 libs build. However in that case the fault is potentially more subtle, because the library is then being linked with a dependency on the *system* libstdc++.dylib and not the current build.
