cgen: cleanup spawn_and_go and fix #23390

[felipensp]

Cleanup
Fix #23390

_{Huly®: V_0.6-21823}

[spytheman]

Excellent work.

[felipensp]

Excellent work.

It is failing on musl, should add an ignore clause there?

[spytheman]

No, please leave it as it is for now.
I would like to reproduce it locally first, to see the actual difference.

[spytheman]

Locally, after installing diffutils:

vlib/v/slow_tests/inout/thread_uninitialized_err.vv FAIL
------------------------------------------------------------------- difference: -----------------------------------------------------------------
--- /tmp/v/257500873191573/base 2025-01-07 11:54:50.125835442 +0000
+++ /tmp/v/257500873191573/target       2025-01-07 11:54:50.125835442 +0000
@@ -1,2 +1,2 @@
 ================ V panic ================
-V panic: unable to join thread
+0x7ff94e6d3404: at ???: RUNTIME ERROR: invalid memory access
-------------------------------------------------------------------------------------------------------------------------------------------------