As noted in <https://github.com/llvm/llvm-project/pull/78537>, MSVC
places import descriptors in both the EC and regular map - that PR moved
the descriptors to ONLY the regular map, however this causes linking
errors when linking as Arm64EC:
```
bcryptprimitives.lib(bcryptprimitives.dll) : error LNK2001: unresolved external symbol __IMPORT_DESCRIPTOR_bcryptprimitives (EC Symbol)
```
This change copies import descriptors from the regular map to the EC
map, which fixes this linking error.
1a6ec906fb