pkg/54277: firefox 67.0.1 clang(base+pkgsrc): /usr/include/c++/cmath:393:12: error: use of undeclared identifier '__isinf'

[ng0%n0.is@localhost]

>Number:         54277
>Category:       pkg
>Synopsis:       firefox 67.0.1 clang(base+pkgsrc): /usr/include/c++/cmath:393:12: error: use of undeclared identifier '__isinf'
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 06 09:45:00 +0000 2019
>Originator:     ng0
>Release:        current
>Organization:
>Environment:
NetBSD uptimegirl 8.99.42 NetBSD 8.99.42 (GENERIC) amd64

>Description:
This system runs both pkgsrc and base with clang from base.
While building firefox from pkgsrc, this error is encountered.

In file included from /usr/work/www/firefox/work/firefox-67.0.1/mfbt/decimal/Decimal.cpp:32:
In file included from /usr/work/www/firefox/work/firefox-67.0.1/mfbt/decimal/moz-decimal-utils.h:16:
In file included from /usr/work/www/firefox/work/build/dist/include/mozilla/FloatingPoint.h:15:
In file included from /usr/work/www/firefox/work/build/dist/include/mozilla/MathAlgorithms.h:15:
In file included from /usr/work/www/firefox/work/build/dist/system_wrappers/cmath:3:
/usr/include/c++/cmath:393:12: error: use of undeclared identifier '__isinf'
    return isinf(__lcpp_x);
           ^
/usr/include/math.h:484:20: note: expanded from macro 'isinf'
#define isinf(__x)      __isinf(__x)
                        ^
/usr/include/c++/cmath:403:12: note: in instantiation of function template specialization '__libcpp_isinf<double>' requested here
    return __libcpp_isinf((typename std::__promote<_A1>::type)__lcpp_x);
           ^
/usr/work/www/firefox/work/firefox-67.0.1/mfbt/decimal/Decimal.cpp:698:14: note: in instantiation of function template specialization 'isinf<double>' requested here
    if (std::isinf(doubleValue))
             ^
1 error generated.
gmake[3]: *** [/usr/work/www/firefox/work/firefox-67.0.1/config/rules.mk:807: Decimal.o] Error 1
gmake[3]: Leaving directory '/usr/work/www/firefox/work/build/mfbt'
gmake[2]: *** [/usr/work/www/firefox/work/firefox-67.0.1/config/recurse.mk:74: mfbt/target] Error 2
gmake[2]: Leaving directory '/usr/work/www/firefox/work/build'
gmake[1]: *** [/usr/work/www/firefox/work/firefox-67.0.1/config/recurse.mk:34: compile] Error 2
gmake[1]: Leaving directory '/usr/work/www/firefox/work/build'
gmake: *** [/usr/work/www/firefox/work/firefox-67.0.1/config/rules.mk:400: all] Error 2
*** Error code 2

Stop.
make[1]: stopped in /usr/pkgsrc/www/firefox
*** Error code 1

Stop.
make: stopped in /usr/pkgsrc/www/firefox

>How-To-Repeat:

>Fix: