[PATCH 0/1] MR3734: tools: Use posix_spawn() instead of fork()/execvp().

[Brendan Shanks (＠bshanks)]

`posix_spawn()` should be more efficient on all systems, especially macOS. Running `make -j12 install` in an x86_64 emulated shell on a 12-core M2 Pro system, I saw a substantial time improvement (9 minutes vs 13) and much lower system overhead.