Preserve optimization flags

aws-lc-sys/builder/cmake_builder.rs

@@ -158,6 +158,11 @@ impl CmakeBuilder {
             env::set_var("CFLAGS", cflags);
         }
 
+        // cmake-rs has logic that strip Optimization/Debug options that be passed via CFLAGS.
+        // This breaks the build for build configurations that generate warnings when optimizations
+        // are disabled.
+        self.preserve_cflag_optimization_flags(&mut cmake_cfg);
+
         // Allow environment to specify CMake toolchain.
         let toolchain_var_name = format!("CMAKE_TOOLCHAIN_FILE_{}", target_underscored());
         if let Some(toolchain) =
@@ -206,6 +211,18 @@ impl CmakeBuilder {
         cmake_cfg
     }
 
+    fn preserve_cflag_optimization_flags(&self, cmake_cfg: &mut cmake::Config) {
+        if let Ok(cflags) = env::var("CFLAGS") {
+            let split = cflags.split("\\s+");
+            for arg in split {
+                if arg.starts_with("-O") || arg.starts_with("/O") {
+                    emit_warning(&format!("Preserving optimization flag: {arg}"));
+                    cmake_cfg.cflag(arg);
+                }
+            }
+        }
+    }
+
     #[allow(clippy::unused_self)]
     fn configure_android(&self, _cmake_cfg: &mut cmake::Config) {
         // If we leave CMAKE_SYSTEM_PROCESSOR unset, then cmake-rs should handle properly setting