- libproj thirdparty in VTK uses `-Werror` and called
 `check_c_source_compiles` to test for `PTHREAD_MUTEX_RECURSIVE`
- in release build for wasm64 arch, clang emitted a warning
  `-Wlimited-postlink-optimizations` only in 64 bit
  which was treated as an error (because of the `-Werror`)
- we negate that warning in the dockerfile.