...post 68e2a4e4 "Revert 'Visibility doesn't
seem to work as we want in Apple's Clang.'"

Quoting <https://developer.apple.com/library/mac/documentation/developertools/
Conceptual/CppRuntimeEnv/Articles/SymbolVisibility.html> section "Symbol
Visibility and Objective-C:"  "When building for x86_64 OS X or for iOS, symbol
visibility /does/ affect objective-C classes.  [...]  This means that if a given
class is intended to be usable outside the library or executable it's defined
in, you need to ensure proper symbol visibility."

The chosen syntax works at least with both --en/disable-64-bit "experimental"
(Clang-based) builds on OS X 10.8.  Hopefully, it also works for baseline
builds.  (Also, it could be that a more fine grained use of
SAL_DLLPUBLIC_EXPORT/SAL_DLLPRIVATE would be useful, but with the current setup
at least linking of Library_vcl against Library_AppleRemote works.)

Change-Id: Iff4fe9e50d1400c83879f62fe29b35bd19d58eb8