no silent error when locating libraries (enhancement)

[Alexander-Barth]

I am trying to install EzXML, but the installation process failed with the error:

 Error: Error building `EzXML`: 
│ ERROR: LoadError: LibraryProduct(nothing, ["libxml2"], :libxml2, "Prefix(/home/ulg/gher/abarth/.julia/packages/EzXML/3U9Ow/deps/usr)") is not satisfied, cannot generate deps.jl!

The problem was that libxml2.so require libz, but the system libz is too old. It would be great if a user would see the error message of dlopen, instead of failing silently.

https://github.com/JuliaPackaging/BinaryProvider.jl/blob/master/src/Products.jl#L172