GC_mark_lock_holder assertion failure in gctest child on Win64

[ivmai]

Build: https://ci.appveyor.com/project/ivmai/bdwgc/builds/51058497/job/5pl2p03sk61klprr
Source (line):

bdwgc/pthread_support.c

Line 3008 in b48c425

GC_ASSERT(GC_mark_lock_holder != NUMERIC_THREAD_ID(pthread_self()));

Host: Windows 64
Config: TARGET=cmake-msys, CMAKE_OPTIONS=-DCMAKE_BUILD_TYPE=Debug -DBUILD_SHARED_LIBS=OFF -Dbuild_tests=ON -Denable_cplusplus=ON -Denable_gc_assertions=ON -Dinstall_headers=OFF -Denable_rwlock=ON, CMAKE_CONFIG=Release
Output (gctest):

Assertion failure: /C/projects/bdwgc/pthread_support.c:3008
Child process failed, pid= 648, status= 0x6
Test failed