MKLLVM build of -current fails because of pthread_types.h

[Thomas Klausner <tk%giga.or.at@localhost>]

My command line

build.sh -j 32 -x -V MKDEBUG=yes -V MKDEBUGLIB=yes -V MKLLVM=yes -V NOGCCERROR=yes -m amd64 distribution

fails with:

--- shared_mutex.o ---
In file included from /usr/src/external/bsd/libc++/dist/libcxx/include/shared_mutex:130,
                 from /usr/src/external/bsd/libc++/lib/../dist/libcxx/src/shared_mutex.cpp:14:
/usr/src/external/bsd/libc++/dist/libcxx/include/__mutex_base: In constructor 'constexpr std::__1::condition_variable::condition_variable()':
/usr/src/external/bsd/libc++/dist/libcxx/include/__mutex_base:273:71: error: temporary of non-literal type '__pthread_cond_st' in a constant expression
     constexpr condition_variable() : __cv_(PTHREAD_COND_INITIALIZER) {}
                                                                       ^
In file included from /usr/obj/amd64.gcc.20200617/usr/include/sys/types.h:359,
                 from /usr/obj/amd64.gcc.20200617/usr/include/sys/endian.h:55,
                 from /usr/src/external/bsd/libc++/dist/libcxx/include/__config:82,
                 from /usr/src/external/bsd/libc++/lib/../dist/libcxx/src/shared_mutex.cpp:10:
/usr/obj/amd64.gcc.20200617/usr/include/pthread_types.h:170:8: note: '__pthread_cond_st' is not literal because:
 struct __pthread_cond_st {
        ^~~~~~~~~~~~~~~~~
/usr/obj/amd64.gcc.20200617/usr/include/pthread_types.h:175:17: note:   non-static data member '__pthread_cond_st::ptc_waiters' has volatile type
  void *volatile ptc_waiters;
                 ^~~~~~~~~~~

Please fix :)
 Thomas