-fvisibility=hidden for libX11

[Bernardo Innocenti]

Hello,

I've managed to get libX11 to work with -fvisibility=hidden
for a small load time improvement on ELF systems.

Patches are here:
  https://bugs.freedesktop.org/show_bug.cgi?id=2607

Tested only on Linux, but should work with other systems
too as I'm using the same preprocessor magic used by Mesa.

I'll be glad to port this change to the modular tree
after it's been applied to the monolithic tree.

Any feedback appreciated.

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/