bug#64216: libgnu __spawni fail on Darwin

[Torrekie]

Due to the lack of attaching child process feature in LLDB, I cannot see what was happening after a fork() call, but one thing is clear that the alternative `posix_spawn` provided by lib/spawni.c was not quite working as expected on Darwin systems (might only happens under arm64). 

https://github.com/NanoComp/meep/issues/2495

Same bug mentioned in this GitHub issue, and I have actually attempted to undef REPLACE_POSIX_SPAWN to use system one, but it was still corrupted by malformed file actions which returning 22 (EINVAL) and set errno to ENOENT that may complaining about dup2-ed non-standard stdio fds.

One thing is for sure, when REPLACE_POSIX_SPAWN is defined, posix_spawn calls will point to __spawni function as implementation. This function fails before actually calling `execve` (Or I didn't successfully caught that in lldb)

This was my test result on macOS 11.2 arm64

/Applications/Xcode.app/Contents/Developer/usr/bin/make  check-TESTS

test-system-cmds: system* exit status was 127 rather than 42

FAIL: test-system-cmds

PASS: test-bad-identifiers

PASS: test-require-extension

PASS: test-guile-snarf

PASS: test-import-order

PASS: test-command-line-encoding

PASS: test-command-line-encoding2

PASS: test-language

error: interrupted by the user

PASS: test-guild-compile

wrote `/Users/torrekie/proj/guile-3.0.9/cache/guile/ccache/3.0-LE-8-4.6/Users/torrekie/proj/guile-3.0.9/test-suite/standalone/test-signal-fork.go'

parent: 53087

....child: ..53133

.............................................

completed

PASS: test-signal-fork

PASS: test-num2integral

PASS: test-round

PASS: test-asmobs

PASS: test-ffi

PASS: test-foreign-object-scm

PASS: test-foreign-object-c

PASS: test-list

PASS: test-unwind

PASS: test-conversion

PASS: test-loose-ends

PASS: test-fast-slot-ref

PASS: test-mb-regexp

PASS: test-use-srfi

PASS: test-scm-c-read

PASS: test-scm-take-locale-symbol

PASS: test-scm-take-u8vector

PASS: test-scm-to-latin1-string

PASS: test-scm-values

PASS: test-scm-c-bind-keyword-arguments

PASS: test-srfi-4

PASS: test-extensions

PASS: test-with-guile-module

PASS: test-scm-with-guile

PASS: test-scm-spawn-thread

PASS: test-pthread-create

SKIP: test-pthread-create-secondary

PASS: test-smob-mark

PASS: test-smob-mark-race

wrote `/Users/torrekie/proj/guile-3.0.9/cache/guile/ccache/3.0-LE-8-4.6/Users/torrekie/proj/guile-3.0.9/test-suite/standalone/test-stack-overflow.go'

SKIP: test-stack-overflow

wrote `/Users/torrekie/proj/guile-3.0.9/cache/guile/ccache/3.0-LE-8-4.6/Users/torrekie/proj/guile-3.0.9/test-suite/standalone/test-out-of-memory.go'

SKIP: test-out-of-memory

;;; (child-exception ("scm_fdes_to_port" "~A" ("Bad file descriptor") (9)))

;;; (child-status 256)

PASS: test-close-on-exec

==================================

1 of 38 tests failed

(3 tests were not run)

Please report to bug-guile@gnu.org

==================================

make[5]: *** [check-TESTS] Error 1

make[4]: *** [check-am] Error 2

make[3]: *** [check] Error 2

make[2]: *** [check-recursive] Error 1

make[1]: *** [check-recursive] Error 1

make: *** [check] Error 2