* Update `__chkstk_ms` to have weak linkage
`__chkstk_ms` was causing conflicts during linking in some circumstances (specifically with linking object files from Rust sources). This PR switches `__chkstk_ms` to have weak linkage.
#15107
* Update stack_probe.zig to weak linkage for all symbols
stage2: change logic for detecting whether the main package is inside
the std package. Previously it relied on realpath() which is not portable.
This uses resolve() which is how imports already work.
* stage2: fix cleanup bug when creating Module
* flatten lib/std/special/* to lib/*
- this was motivated by making main_pkg_is_inside_std false for
compiler_rt & friends.
* rename "mini libc" to "universal libc"
