Another patch for visibility.

[NIIBE Yutaka]

Hi H.J., 

H . J . Lu wrote:
 > One more thing, we should add more tests to ld/testsuite/ld-elfvsb. I
 > will try when I find time. Any contributions are more than welcome.

Currently, I'm working for supporting visibility bits with GCC, by the
function/variable attribute.

I've sent initial patch to gcc-patches@gnu.gcc.org, and now trying to 
implement:

	__attribute__ ((visibility(internal)))
	__attribute__ ((visibility(hidden)))
	__attribute__ ((visibility(protected)))

Any comments are appriciated.
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