Merging r375077:

------------------------------------------------------------------------
r375077 | sbc | 2019-10-16 20:21:02 -0700 (Wed, 16 Oct 2019) | 10 lines

[lld][WebAssembly] Fix for weak references to data symbols in archives

Fix a bug where were not handling relocations against weakly undefined
data symbol.  Add a test for this case.  Also ensure that the weak
references to data symbols are not pulled in from archive files by
default (but are if `-u <name>` is added to the command line).

Fixes: PR43696

Differential Revision: https://reviews.llvm.org/D69073
------------------------------------------------------------------------