`int isnan(double)` is a POSIXism
- `isnan` is something relatively new. We need to provide one for
those systems without it. However:
- X/Open defines `int isnan(double)`. Note the `int`.
- C99 defines `isnan(x)` to be a macro.
- C++11 nukes them all, undefines all the "masking macro"s, and
defines its own `bool isnan(double)`. Note the `bool`.
- In C++, `int isnan(double)` and `bool isnan(double)` are
incompatible.
- So the mess.
[Bug #14816][ruby-core:87364]
further reading: https://developers.redhat.com/blog/2016/02/29/why-cstdlib-is-more-complicated-than-you-might-think/
include/ruby/missing.h: defined(__cplusplus) before using __cplusplus
* include/ruby/missing.h (isinf, isnan): For non-C++ programs,
defined(__cplusplus) may be needed before using __cplusplus.
[Bug #14816]
merge revision(s) 63571,63572: [Backport #14816]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@64434 b2dd03c8-39d4-4d8f-98ff-823fe69b080e