Replace windows-sys with a dummy crate in the library workspace

This reduces the vendor size of the standard library from 37MB to 20MB.

library/Cargo.lock

@@ -347,7 +347,7 @@ dependencies = [
  "wasip1",
  "wasip2",
  "wasip3",
- "windows-link 0.0.0",
+ "windows-link",
 ]
 
 [[package]]
@@ -443,20 +443,9 @@ dependencies = [
 name = "windows-link"
 version = "0.0.0"
 
-[[package]]
-name = "windows-link"
-version = "0.2.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
-
 [[package]]
 name = "windows-sys"
-version = "0.61.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
-dependencies = [
- "windows-link 0.2.1",
-]
+version = "0.61.100"
 
 [[package]]
 name = "wit-bindgen"

library/Cargo.toml

@@ -85,3 +85,6 @@ rustflags = [
 rustc-std-workspace-core = { path = 'rustc-std-workspace-core' }
 rustc-std-workspace-alloc = { path = 'rustc-std-workspace-alloc' }
 rustc-std-workspace-std = { path = 'rustc-std-workspace-std' }
+
+# See comments in `library/windows-sys/Cargo.toml` for why this is patched
+windows-sys = { path = 'windows-sys' }

library/windows-sys/Cargo.toml

@@ -0,0 +1,16 @@
+# dlmalloc has a dependency on windows-sys for when it gets compiled for Windows.
+# std however never actually uses dlmalloc on Windows. As dlmalloc is the only
+# user of windows-sys in the standard library, the windows-sys crate unnecessarily
+# increases the size of the vendored crates. By replacing it with an empty crate
+# we save about 19MB.
+
+[package]
+name = "windows-sys"
+version = "0.61.100"
+edition = "2024"
+
+[features]
+Win32_Foundation = []
+Win32_System_Memory = []
+Win32_System_Threading = []
+Win32_System_SystemInformation = []

library/windows-sys/src/lib.rs

@@ -0,0 +1 @@
+compile_error!("This crate should never be compiled");

src/tools/tidy/src/deps.rs

@@ -543,7 +543,7 @@ const PERMITTED_STDLIB_DEPENDENCIES: &[&str] = &[
     "wasip2",
     "wasip3",
     "windows-link",
-    "windows-sys",
+    "windows-sys@0.61.100", // Enforce the usage of our dummy windows-sys patch. Keep version in sync.
     "wit-bindgen",
     // tidy-alphabetical-end
 ];