Skip bindgen 0.70's layout tests before Rust 1.77

Cargo.toml

@@ -49,3 +49,4 @@ openssl-macros = "0.1.1"
 tower = "0.4"
 tower-layer = "0.3"
 tower-service = "0.3"
+autocfg = "1.3.0"

boring-sys/Cargo.toml

@@ -77,6 +77,7 @@ pq-experimental = []
 underscore-wildcards = []
 
 [build-dependencies]
+autocfg = { workspace = true }
 bindgen = { workspace = true }
 cmake = { workspace = true }
 fs_extra = { workspace = true }

boring-sys/build/main.rs

@@ -687,6 +687,10 @@ fn main() {
         }
     });
 
+    // bindgen 0.70 replaced the run-time layout tests with compile-time ones,
+    // but they depend on std::mem::offset_of, stabilized in 1.77.
+    let supports_layout_tests = autocfg::new().probe_rustc_version(1, 77);
+
     let mut builder = bindgen::Builder::default()
         .rust_target(bindgen::RustTarget::Stable_1_68) // bindgen MSRV is 1.70, so this is enough
         .derive_copy(true)
@@ -701,7 +705,7 @@ fn main() {
         .generate_comments(true)
         .fit_macro_constants(false)
         .size_t_is_usize(true)
-        .layout_tests(true)
+        .layout_tests(supports_layout_tests)
         .prepend_enum_name(true)
         .blocklist_type("max_align_t") // Not supported by bindgen on all targets, not used by BoringSSL
         .clang_args(get_extra_clang_args_for_bindgen(&config))