libstdc++-v3 configure checks whether old glibc inline definitions
of isnan would conflict with the libstdc++-v3 definitions and
works around them if so. But if g++ 6.x build A is used to build
another g++ 6.x B, the configure step for B will pick up the math.h
installed alongside A instead of the glibc version. configure will
then assume that the workaround isn't necessary, leaving B with a
broken cmath.
isinf already worked around this. This patch extends the same fix
to isnan. (Thanks to George for the fix.)
libstdc++-v3/
2017-03-10 George Lander <george.lander@arm.com>
* acinclude.m4 (glibcxx_cv_obsolete_isnan): Define
_GLIBCXX_INCLUDE_NEXT_C_HEADERS before including math.h.
* configure: Regenerate.
From-SVN: r246025
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