libshared: Enable hidden visibility.

This breaks ABI as we forgot to do this originally and a lot of apps
implicitly use symbols from libbe or elsewhere that are imported from
libshared, but we are about to branch beta4, so now is the time to
change this.

Fixes #17256.

src/kits/shared/Jamfile

@@ -24,10 +24,6 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 		# for BKeymap
 		UsePrivateHeaders interface ;
 
-		# FIXME: These symbols should be hidden, but too many applications depend
-		# on them at present for that.
-		NO_HIDDEN_VISIBILITY on <$(architecture)>libshared.a = 1 ;
-
 		StaticLibrary <$(architecture)>libshared.a :
 			AboutMenuItem.cpp
 			ArgumentVector.cpp