In the case of weakly defined symbols in shared libraries we now
generate both an import and an export. The dynamic linker can then
choose how a winner from among all the shared libraries that define a
given symbol.
Previously any direct usage of a weakly defined symbol would use the
DSO-local definition (For example, even through there would be single
address for a weakly defined function, each DSO could end up directly
calling its local version).
Fixes: https://github.com/emscripten-core/emscripten/issues/13773
Differential Revision: https://reviews.llvm.org/D108413
Sam Clegg