[MacPorts] #66978: LegacySupport messes up isnan with GCC (and isinfinity): error: 'isnan' was not declared in this scope; did you mean 'std::isnan'

[MacPorts]

#66978: LegacySupport messes up isnan with GCC (and isinfinity): error: 'isnan' was
not declared in this scope; did you mean 'std::isnan'
----------------------------+--------------------------
  Reporter:  barracuda156   |      Owner:  cjones051073
      Type:  defect         |     Status:  assigned
  Priority:  Normal         |  Milestone:
 Component:  ports          |    Version:  2.8.1
Resolution:                 |   Keywords:
      Port:  legacysupport  |
----------------------------+--------------------------

Comment (by kencu):

 see:

 https://github.com/igraph/rigraph/issues/669

 and this reproducer is mentioned:

 https://github.com/igraph/rigraph/issues/669#issuecomment-1426711903

 and also this:

 https://developers.redhat.com/blog/2016/02/29/why-cstdlib-is-more-
 complicated-than-you-might-think

 This could have something to do with the math modifications in
 legacysupport... they have been very complicated to sort out exactly
 correctly. A number of folks have had a stab at it, and there are still
 issues. There is an open PR to fix an issue with clang building against
 libstdc++ that is still not fully sorted out after some many weeks.

-- 
Ticket URL: <https://trac.macports.org/ticket/66978#comment:3>
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