Build error on Alpine linux (musl libc)

[riza]

When building on Alpine linux, this error was raised:

../src/pj/os_core_unix.c: In function 'init_mutex':
../src/pj/os_core_unix.c:1107:40: error: 'PTHREAD_MUTEX_FAST_NP' undeclared (first use in this function)
  rc = pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_FAST_NP);
                                        ^

It seems that PTHREAD_MUTEX_FAST_NP and PTHREAD_MUTEX_RECURSIVE_NP is not portable, as the NP suffix indicates a non-portable extension to the POSIX standard.

Reference:

• ​http://www.unix.com/man-page/POSIX/3posix/pthread_mutexattr_settype/
• ​http://www.agr.unideb.hu/~agocs/informatics/11_e_unix/unixhelp/unixhelp.ed.ac.uk/CGI/man-cgid5de.html?pthread_mutexattr_settype

Next error was due to the use of an internal struct field
__sched_priority:

../src/samples/siprtp.c:1136:7: error: 'struct sched_param' has no member named '__sched_priority'
     tp.__sched_priority = max_prio;
       ^

variables and fields that starts with "__" are for internal use and
should in general not be used in applications.

Reference:

• ​http://pubs.opengroup.org/onlinepubs/007904975/basedefs/sched.h.html
• ​http://code.metager.de/source/xref/google/chromiumos/third_party/glibc/posix/sched.h#34

[riza]

In 5277:

Fixed #1912: Build Error on Alpine linux (musl libc).