std_detect: Use rustc-std-workspace-* to pull in compiler-builtins

#145489 changed `std_detect` to no
longer depend on `cfg-if`, which meant it no longer indirectly pulled in
`rustc-std-workspace-core` via `cfg-if`. That caused it to no longer
depend on `compiler-builtins`.

Change `std_detect` to use `rustc-std-workspace-core` and
`rustc-std-workspace-alloc`, to integrate with the rustc workspace. This
also pulls in `compiler-builtins` via `rustc-std-workspace-core`.

Closes: #145594

Author: joshtriplett

library/std_detect/Cargo.toml

@@ -21,8 +21,8 @@ is-it-maintained-open-issues = { repository = "rust-lang/stdarch" }
 maintenance = { status = "experimental" }
 
 [dependencies]
-core = { path = "../core" }
-alloc = { path = "../alloc" }
+core = { version = "1.0.0", package = 'rustc-std-workspace-core' }
+alloc = { version = "1.0.0", package = 'rustc-std-workspace-alloc' }
 
 [target.'cfg(not(windows))'.dependencies]
 libc = { version = "0.2.0", optional = true, default-features = false }