fix(cxx_zig_toolchain): resolve wrapper paths and expand nested argsfiles

[cehoffman]

CGO builds with zig toolchain fail because go_go_wrapper changes to a temp directory before invoking the C compiler. The generated wrapper scripts use relative paths that break once we're no longer in the project root:

# runtime/cgo
zig_cc.sh: line 2: buck-out/v2/gen/mise/.../zig: No such file or directory

After fixing that, zig also doesn't support nested argsfiles which the Go prelude generates:

error: unable to parse command line parameters: NestedResponseFile

This PR uses BASH_SOURCE to resolve paths from the script's location and adds recursive argsfile expansion before invoking zig.

The Windows path has the same issues but I don't have a way to test batch scripts. Would need %~dp0 for path resolution and similar expansion logic - happy to add it if someone can validate.

[meta-codesync]

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