Support cross compiling with prebuilt NASM (#528)

* Support cross compiling to x86_64-pc-windows-gnu

* Update aws-lc-sys/builder/prebuilt-nasm.sh

Co-authored-by: Sean McGrail <549813+skmcgrail@users.noreply.github.com>

---------

Co-authored-by: Sean McGrail <549813+skmcgrail@users.noreply.github.com>

.github/workflows/cross.yml

@@ -269,3 +269,20 @@ jobs:
              . "$HOME/.cargo/env"
             cargo test -p aws-lc-rs
             cargo test -p aws-lc-rs --no-default-features --features=fips
+  cross-x86_64-pc-windows-gnu:
+    if: github.repository_owner == 'aws'
+    name: cross (prebuilt nasm) - x86_64-pc-windows-gnu
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: 'recursive'
+      - uses: dtolnay/rust-toolchain@stable
+        id: toolchain
+        with:
+          toolchain: 'stable'
+          target: x86_64-pc-windows-gnu
+      - name: Install mingw
+        run: sudo apt-get update && sudo apt-get install --assume-yes mingw-w64
+      - name: Run cargo test
+        run: cargo build -p aws-lc-rs --features prebuilt-nasm --target x86_64-pc-windows-gnu

aws-lc-sys/builder/cmake_builder.rs

@@ -256,10 +256,16 @@ impl CmakeBuilder {
             emit_warning("!!!   Using pre-built NASM binaries   !!!");
             emit_warning("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
 
+            let script_name = if cfg!(target_os = "windows") {
+                "prebuilt-nasm.bat"
+            } else {
+                "prebuilt-nasm.sh"
+            };
+
             let script_path = self
                 .manifest_dir
                 .join("builder")
-                .join("prebuilt-nasm.bat")
+                .join(script_name)
                 .display()
                 .to_string();
             let script_path = script_path.replace('\\', "/");

aws-lc-sys/builder/prebuilt-nasm.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0 OR ISC
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        -o)
+            shift
+            path="$1"
+            filename="$(basename "$path")"
+            filename="$(echo "$filename" | cut -f 1 -d '.')"
+            cp "$SCRIPT_DIR/prebuilt-nasm/${filename}".obj "$path"
+            exit 0
+            ;;
+        *)
+            shift
+            ;;
+    esac
+done
+
+# If we reach here, it means we didn't find the -o option
+echo "PATH: $path" >&2
+echo "FILENAME: $filename" >&2
+echo "SCRIPT_DIR: $SCRIPT_DIR" >&2
+exit 1