Problems with C++ compiler on 9.0_RC2

[Marc Baudoin <babafou%babafou.eu.org@localhost>]

Hi,

I recently upgraded a NetBSD/amd64 8.1 system to 9.0_RC2 and I
noticed problems when compiling C++ programs.

For instance, with pkgsrc/devel/cmake:

In file included from /usr/include/g++/memory:74:0,
                 from cmake_bootstrap_13004_test.cxx:3:
/usr/include/g++/ext/concurrence.h:124:5: error: '__gthread_mutex_t' does not name a type; did you mean '__pthread_mutex_st'?
     __gthread_mutex_t _M_mutex;
     ^~~~~~~~~~~~~~~~~
     __pthread_mutex_st
/usr/include/g++/ext/concurrence.h:169:5: error: '__gthread_mutex_t' does not name a type; did you mean '__pthread_mutex_st'?
     __gthread_mutex_t* gthread_mutex(void)
     ^~~~~~~~~~~~~~~~~
     __pthread_mutex_st
/usr/include/g++/ext/concurrence.h:179:5: error: '__gthread_recursive_mutex_t' does not name a type; did you mean '__recursive_mutex'?
     __gthread_recursive_mutex_t _M_mutex;
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
[...]

or with pkgsrc/print/poppler:

In file included from /usr/include/g++/mutex:43:0,
                 from /usr/pkgsrc/print/poppler/work/poppler-0.84.0/poppler/Array.h:32,
                 from /usr/pkgsrc/print/poppler/work/poppler-0.84.0/poppler/Object.h:335,
                 from /usr/pkgsrc/print/poppler/work/poppler-0.84.0/poppler/Annot.cc:61:
/usr/include/g++/bits/std_mutex.h:63:13: error: '__gthread_mutex_t' does not name a type; did you mean '__pthread_mutex_st'?
     typedef __gthread_mutex_t   __native_type;
             ^~~~~~~~~~~~~~~~~
             __pthread_mutex_st
/usr/include/g++/bits/std_mutex.h:70:5: error: '__native_type' does not name a type; did you mean '__false_type'?
     __native_type  _M_mutex;
     ^~~~~~~~~~~~~
     __false_type
/usr/include/g++/bits/std_mutex.h: In constructor 'std::__mutex_base::__mutex_base()':
/usr/include/g++/bits/std_mutex.h:75:38: error: '_M_mutex' was not declared in this scope
       __GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);
                                      ^~~~~~~~

Is it a problem with my setup, with pkgsrc or is there something
wrong with the C++ environment in 9.0_RC2?