Default umask 0o777 is too strict

[tiran]

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.12 (38d1292ba2f5b4a7c8518931f5ae6f97ef0f6827)
clang version 15.0.0 (https://github.com/llvm/llvm-project d58cc0839ee5935e649dbbc18c898a8e4bcd6724)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin

Emscripten defines the default umask as 0777:

emscripten/system/lib/libc/emscripten_syscall_stubs.c

Line 31 in 854adf6

static mode_t g_umask = S_IRWXU | S_IRWXG | S_IRWXO;

The issue was reported before as #9916. The strict umask causes some test failures in CPython test suite on Node with NODERAWFS, because some files are created with permissions 000. I have not noticed the problem before because I was running the tests in a containerized environment with effective user root. Root has DAC override capability and can access files with permission 000.

A better default umask would be 0027 or 0002.