(ITS#8481) macOS shared libraries should be .dylib not .so

[ilovezfs@icloud.com]

Full_Name: ilovezfs
Version: LMDB_0.9.18
OS: macOS
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (50.168.32.161)


This is in regard to the Homebrew formula for LMDB (See
https://github.com/Homebrew/homebrew-core/pull/2317). Currently, we are having
to patch the shared library extensions from .so to .dylib, which is the correct
file extension on macOS. It would be great if this patch could be removed from
the formula, which would mean upstream support for automatically setting the
extension correctly based on platform in the build system.

This is a pretty common practice, and it would be highly appreciated as we like
to as little patching as possible to upstream code for maintainability and
fidelity.

In particular, we're currently having to do the following replacement:
```
 inreplace "Makefile", ".so", ".dylib"
```

Here's a typical example of how shared libraries get named on macOS: 
```
libiconv.2.4.0.dylib -> libiconv.2.dylib
libiconv.2.dylib
libiconv.dylib -> libiconv.2.4.0.dylib
```