Restructure the way libpam-sys-impls works to fix cross-compilation. The previous structure of libpam-sys-impls meant that things got confusing (including for me) between what constants were build-time and what constants were run-time. This broke cross-compilation. This simplifies the way that works so that `libpam-sys-impls` has *no* build script itself and is intended mostly as a library to be included in other libraries' build scripts (while also exporting the PamImpl enum).

[package]
name = "libpam-sys-test"
version.workspace = true
edition.workspace = true
rust-version.workspace = true
publish = false
readme = "README.md"

[dependencies]
libc = "0.2"
libpam-sys = { path = ".." }

[build-dependencies]
bindgen = "0.72.0"
ctest = "0.4.11"
libpam-sys = { path = ".." }
libpam-sys-impls = { path = "../libpam-sys-impls" }
proc-macro2 = "1.0.95"
quote = "1.0.40"
syn = { version = "2.0.104", features = ["full"] }