This is actually inside luv and may only happen on Windows (?). Anyway, here's the warning:
[2/52] Compiling Runtime/luvi_compat.c ...
In file included from Runtime/luvi_compat.c:11:
deps/luv/deps/lua-compat-5.3/lprefix.h: In function 'compat53_utf8_escape':
deps/luv/deps/lua-compat-5.3/lprefix.h:69:16: warning: comparison of integer expressions of different signedness: 'long int' and 'unsigned int' [-Wsign-compare]
69 | } while (x > mfb);
| ^
This is actually inside luv and may only happen on Windows (?). Anyway, here's the warning: