[v3] Disable gthreads on Solaris 8/9 (PR libstdc++/52189)

[Rainer Orth]

As discussed the improved/relaxed test for gthreads support breaks
symbol versioning on Solaris 8 and 9.  The best solution seems to
disable it by default on those targets, allowing users to reenable it if
they don't care about compatibility.

The following patch does just that, disabling only if symbol versioning
is active, and warning if users choose to enable it nonetheless.

I had to move the GLIBCXX_CHECK_GTHREADS down in configure.ac, adding a
dependency in acinclude.m4 didnd't suffice.

Bootstrapped without regressions on {sparc-sun,i386-pc}-solaris2.{8, 9,
10, 11} and x86_64-unknown-linux-gnu, verifying that there's no change
on Linux/x86_64 and the gthr-related symbols are gone on Solaris 8 and 9
only.

Ok for mainline?

Btw., the ChangeLog lies at one point: I didn't include the
configure.html update since I lack the required tools.  I'd appreciate
it if some of the libstdc++ maintainers could handle this for me after
checking.

Thanks.
	Rainer


2012-02-12  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	PR libstdc++/52189
	* acinclude.m4 (GLIBCXX_CHECK_GTHREADS): Handle --enable-gthreads.
	Disable on Solaris 8/9 with symbol versioning.
	* configure.ac (GLIBCXX_CHECK_GTHREADS): Move after
	GLIBCXX_ENABLE_SYMVERS.
	* configure: Regenerate.
	* doc/xml/manual/configure.xml (--enable-gthreads): Explain.
	* doc/html/manual/configure.html: Regenerate.

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Rainer Orth, Center for Biotechnology, Bielefeld University