nptl: pthread_mutex_getprioceiling.c is not compiled

[shengyong]

hi, all
When I call pthread_mutex_getprioceiling(), the failure shows that the function
is not implemented.  I checked libpthread/nptl/Makefile.in, and found that
pthread_mutex_getprioceiling.c and pthread_mutex_setprioceiling.c were not compiled.

There is no config option to enable compiling these c files. Should an option, say,
UCLIBC_PTHREAD_CEILING, be added? or just modify the Makefile.in to enforce compiling
them?

thx,
Sheng Yong