In general, if libX.so depends on libY.a, we don't want libY's symbolsdynamically exported by libX. We want libX's use of libY to be private.We use two mechanisms for making this happen. -fvisibility=hidden, whichworks on the build of libY to mark the symbols themselves as hidden inthe object file, and -Wl,--exclude-libs=ALL, which works on the build oflibX to instruct the linker not to re-export symbols from staticlibraries.We set -fvisibility=hidden on some platforms but not all. We use-Wl,--exclude-libs=ALL on the build of Python itself on all platforms,which up to this point built our only dynamic objects (bin/python andlibpython). Now that libtcl and libtk are dynamic, we need to do thesame thing.I'm not sure if -fvisibility=hidden actually does anything useful forus, given the use of -Wl,--exclude-libs=ALL, and I think the fact thatit's only set on some platforms is an oversight and demonstrates thatit's not needed. See#735, which removes it; the builds pass vaildation.