* c-common.c (handle_visibility_attribute): Accept "default".

	* c-common.c (handle_visibility_attribute): Accept "default".
	* tree.h (enum symbol_visibility): New.
	(decl_visibility): Declare.
	* target.h (gcc_target.visibility): Take visibility arg as integer.
	* varasm.c (default_assemble_visibility): Likewise.
	(decl_visibility): New.
	(maybe_assemble_visibility): Use it.
	* output.h (default_assemble_visibility): Update prototype.
	* config/rs6000/rs6000.c (rs6000_assemble_visibility): Take
	visibility arg as integer.
	* doc/extend.texi: Document default visibility.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@59560 138bc75d-0d04-0410-961f-82ee72b054a4