Tor doesn't produce a backtrace on gcc x86_64 on macOS

$ gcc-mp-4.9 -v
Using built-in specs.
COLLECT_GCC=gcc-mp-4.9
COLLECT_LTO_WRAPPER=/opt/local/libexec/gcc/x86_64-apple-darwin15/4.9.3/lto-wrapper
Target: x86_64-apple-darwin15
Configured with: /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc49/gcc49/work/gcc-4.9.3/configure --prefix=/opt/local --build=x86_64-apple-darwin15 --enable-languages=c,c++,objc,obj-c++,lto,fortran,java --libdir=/opt/local/lib/gcc49 --includedir=/opt/local/include/gcc49 --infodir=/opt/local/share/info --mandir=/opt/local/share/man --datarootdir=/opt/local/share/gcc-4.9 --with-local-prefix=/opt/local --with-system-zlib --disable-nls --program-suffix=-mp-4.9 --with-gxx-include-dir=/opt/local/include/gcc49/c++/ --with-gmp=/opt/local --with-mpfr=/opt/local --with-mpc=/opt/local --with-isl=/opt/local --disable-isl-version-check --with-cloog=/opt/local --disable-cloog-version-check --enable-stage1-checking --enable-lto --enable-libstdcxx-time --with-as=/opt/local/bin/as --with-ld=/opt/local/bin/ld --with-ar=/opt/local/bin/ar --with-bugurl=https://trac.macports.org/newticket --with-pkgversion='MacPorts gcc49 4.9.3_0+universal' --with-build-config=bootstrap-debug
Thread model: posix
gcc version 4.9.3 (MacPorts gcc49 4.9.3_0+universal) 
Jacks-Mac:~ twilsonb$ clang-mp-3.7 -v
clang version 3.7.0 (tags/RELEASE_370/final)
Target: x86_64-apple-darwin15.2.0
Thread model: posix

$ src/test/test-bt-cl crash

============================================================ T= 1449767124
Tor  died: Caught signal 11
0   test-bt-cl                          0x0000000108b72178 crash_handler + 56
1   test-bt-cl                          0x0000000108b780de attr_detached + 1374

$ src/test/test-bt-cl assert
Dec 11 04:05:41.826 [err] tor_assertion_failed_(): Bug: src/test/test_bt_cl.c:42: crash: Assertion 1 == 0 failed; aborting. (on Tor 0.2.7.6 )
Dec 11 04:05:41.826 [err] Bug: Assertion 1 == 0 failed in crash at src/test/test_bt_cl.c:42. Stack trace: (on Tor 0.2.7.6 )
Dec 11 04:05:41.826 [err] Bug:     0   test-bt-cl                          0x0000000109fb7264 log_backtrace + 68 (on Tor 0.2.7.6 )