[build] Compensate for libc++ threads errors

LLVM was updated by system update, and is now unhappy building because
of libc++ threads settings. I'm explicitly turning them off in base.yml
for now until I can focus on a better fix.

configs/base.yaml

@@ -12,6 +12,8 @@ variables:
     "-I${source_root}/src/include",
     "-I${source_root}/src/include/x86_64",
     "-fcolor-diagnostics",
+    "-U__STDCPP_THREADS__",
+    "-D_LIBCPP_HAS_NO_THREADS",
     "-DVERSION_MAJOR=${version_major}",
     "-DVERSION_MINOR=${version_minor}",
     "-DVERSION_PATCH=${version_patch}",