Unreviewed libstdc++ patch

[Rainer Orth]

The libstdc++ part of the following patch

	[fixincludes, v3] Don't define libstdc++-internal macros in Solaris 10+ <math.h>
        https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00330.html

has remained unreviewed for a week.  Bruce already approved the
fixincludes part.

In the meantime, full testing on mainline has completed and backports to
the gcc-5 and gcc-6 branches have also been tested successfully.

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University