COMP: some low-level darwin-related patches

- a partial selection from https://github.com/mrklein/openfoam-os-x
  with adjustments. The primary purpose is to reduce header-level
  incompatibilities and to provide a common set of make rules to allow
  easier patching (or re-integration).

src/OpenFOAM/db/dynamicLibrary/dynamicCode/dynamicCode.C

@@ -315,7 +315,11 @@ Foam::fileName Foam::dynamicCode::codeRelPath() const
 
 Foam::fileName Foam::dynamicCode::libRelPath() const
 {
+    #ifdef darwin
+    return codeRelPath()/libSubDir_/"lib" + codeName_ + ".dylib";
+    #else
     return codeRelPath()/libSubDir_/"lib" + codeName_ + ".so";
+    #endif
 }