Hardcoded limit of 16 sasl mechanisms is insufficient on macOS

Thread 1 Crashed:
0   libsystem_kernel.dylib              0x00007fff697c62c6 __pthread_kill + 10
1   libsystem_pthread.dylib             0x00007fff69881bf1 pthread_kill + 284
2   libsystem_c.dylib                   0x00007fff69730745 __abort + 144
3   libsystem_c.dylib                   0x00007fff69730ff3 __stack_chk_fail + 205
4   libqpid-proton-core.10.dylib        0x0000000106d81f89 pni_post_sasl_frame + 1321
5   ???                                 0x00007fd57acb59bb 0 + 140554864908731

$ ../cmake-build-debug/cpp/examples/broker 
broker listening on 5672
=================================================================
==42793==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x70000c4bcbe0 at pc 0x0001013663e1 bp 0x70000c4bc830 sp 0x70000c4bc828
WRITE of size 8 at 0x70000c4bcbe0 thread T3
    #0 0x1013663e0 in pni_split_mechs sasl.c:443
    #1 0x1013646ea in pni_post_sasl_frame sasl.c:480
    #2 0x101357fad in pn_output_write_sasl sasl.c:677
    #3 0x101323909 in transport_produce transport.c:2751
    #4 0x10131ffd3 in pn_transport_pending transport.c:3030
    #5 0x1012b8755 in pn_connection_driver_write_buffer connection_driver.c:120
    #6 0x10120240f in leader_process_pconnection libuv.c:909
    #7 0x1011f8b48 in leader_lead_lh libuv.c:1008
    #8 0x1011f94f3 in pn_proactor_wait libuv.c:1062
    #9 0x10188c55d in proton::container::impl::thread() proactor_container_impl.cpp:753
    #10 0x1018bca31 in void* std::__1::__thread_proxy<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (proton::container::impl::*)(), proton::container::impl*> >(void*) thread:352
    #11 0x7fff6987f2ea in _pthread_body (libsystem_pthread.dylib:x86_64+0x32ea)
    #12 0x7fff69882248 in _pthread_start (libsystem_pthread.dylib:x86_64+0x6248)
    #13 0x7fff6987e40c in thread_start (libsystem_pthread.dylib:x86_64+0x240c)

Address 0x70000c4bcbe0 is located in stack of thread T3 at offset 192 in frame
    #0 0x101363ccf in pni_post_sasl_frame sasl.c:462

  This frame has 3 object(s):
    [32, 48) 'out' (line 464)
    [64, 192) 'mechs' (line 475) <== Memory access at offset 192 overflows this variable
    [224, 228) 'count' (line 478)
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
Thread T3 created by T0 here:
    #0 0x101f5dadd in wrap_pthread_create (libclang_rt.asan_osx_dynamic.dylib:x86_64+0x56add)
    #1 0x1018bc4ab in std::__1::thread::thread<void (proton::container::impl::*)(), proton::container::impl*, void>(void (proton::container::impl::*&&)(), proton::container::impl*&&) thread:368
    #2 0x10188da97 in proton::container::impl::run(int) proactor_container_impl.cpp:802
    #3 0x100f0223c in main broker.cpp:427
    #4 0x7fff6968b3d4 in start (libdyld.dylib:x86_64+0x163d4)

SUMMARY: AddressSanitizer: stack-buffer-overflow sasl.c:443 in pni_split_mechs
Shadow bytes around the buggy address:
  0x1e0001897920: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e0001897930: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e0001897940: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e0001897950: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e0001897960: 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2 00 00 00 00
=>0x1e0001897970: 00 00 00 00 00 00 00 00 00 00 00 00[f2]f2 f2 f2
  0x1e0001897980: 04 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e0001897990: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e00018979a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e00018979b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1e00018979c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==42793==ABORTING
Abort trap: 6

"SRP SRP GS2-IAKERB GS2-KRB5 SCRAM-SHA-1 SCRAM-SHA-256 SCRAM-SHA-256 SCRAM-SHA-1 GS2-KRB5 GS2-IAKERB GSS-SPNEGO GSSAPI GSS-SPNEGO GSSAPI DIGEST-MD5 DIGEST-MD5 OTP OTP NTLM CRAM-MD5 NTLM CRAM-MD5 ANONYMOUS ANONYMOUS"