boring-sys: Support static MSVC runtime

.github/workflows/ci.yml

@@ -226,6 +226,15 @@ jobs:
             RUSTC_BOOTSTRAP: 1 # for -Z checksum-freshness
           # CI's Windows doesn't have required root certs
           extra_test_args: --workspace --exclude tokio-boring --exclude hyper-boring -Z checksum-freshness
+        - thing: x86_64-msvc-static
+          target: x86_64-pc-windows-msvc
+          rust: stable-x86_64-msvc
+          os: windows-latest
+          custom_env:
+            RUSTC_BOOTSTRAP: 1 # for -Z checksum-freshness
+            RUSTFLAGS: -Dwarnings -C target-feature=+crt-static
+          # CI's Windows doesn't have required root certs
+          extra_test_args: --workspace --exclude tokio-boring --exclude hyper-boring -Z checksum-freshness
     env:
       CARGO_HOME: ${{ github.workspace }}/.cache/cargo
       CARGO_BUILD_BUILD_DIR: ${{ github.workspace }}/.cache/build-dir

boring-sys/build/config.rs

@@ -12,6 +12,7 @@ pub(crate) struct Config {
     pub(crate) target_os: String,
     pub(crate) unix: bool,
     pub(crate) target_env: String,
+    pub(crate) target_features: Vec<String>,
     pub(crate) features: Features,
     pub(crate) env: Env,
 }
@@ -51,6 +52,12 @@ impl Config {
         let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap();
         let unix = env::var("CARGO_CFG_UNIX").is_ok();
 
+        let target_features = env::var("CARGO_CFG_TARGET_FEATURE")
+            .unwrap_or_default()
+            .split(',')
+            .map(|s| s.to_owned())
+            .collect();
+
         let features = Features::from_env();
         let env = Env::from_env(&host, &target, features.is_fips_like());
 
@@ -69,6 +76,7 @@ impl Config {
             target_os,
             unix,
             target_env,
+            target_features,
             features,
             env,
         };

boring-sys/build/main.rs

@@ -217,7 +217,11 @@ fn get_boringssl_cmake_config(config: &Config) -> cmake::Config {
         // This is required now because newest BoringSSL requires CMake 3.22 which
         // uses the new logic with CMAKE_MSVC_RUNTIME_LIBRARY introduced in CMake 3.15.
         // https://github.com/rust-lang/cmake-rs/pull/30#issuecomment-2969758499
-        boringssl_cmake.define("CMAKE_MSVC_RUNTIME_LIBRARY", "MultiThreadedDLL");
+        if config.target_features.iter().any(|f| f == "crt-static") {
+            boringssl_cmake.define("CMAKE_MSVC_RUNTIME_LIBRARY", "MultiThreaded");
+        } else {
+            boringssl_cmake.define("CMAKE_MSVC_RUNTIME_LIBRARY", "MultiThreadedDLL");
+        }
     }
 
     if config.host == config.target {