Remove ".dll" from DYNAMICLIB_ENDINGS, since on Windows one never links to a .dll file directly (e.g. via a command line -lFile -> libFile.dll) either, but instead separate import libraries with suffix .lib are used. Note that for crosscompiling, it is _not_ recommended to generate Emscripten static bitcode libraries with suffix .lib, but instead generating files with suffixes .bc (or .a) is better form.
Add comment explaining why .dll is not present in DYNAMICLIB_ENDINGS.
Merge pull request #2498 from juj/no_link_dll

Remove ".dll" from DYNAMICLIB_ENDINGS.