Improve Android support

Author: justsmth

aws-lc-sys/builder/cmake_builder.rs

@@ -130,6 +130,13 @@ impl CmakeBuilder {
             return cmake_cfg;
         }
 
+        if let Some(cc) = option_env("CC") {
+            cmake_cfg.define("CMAKE_C_COMPILER", cc);
+        }
+        if let Some(cxx) = option_env("CXX") {
+            cmake_cfg.define("CMAKE_CXX_COMPILER", cxx);
+        }
+
         // See issue: https://github.com/aws/aws-lc-rs/issues/453
         if target_os() == "windows" {
             Self::configure_windows(&mut cmake_cfg);
@@ -148,6 +155,24 @@ impl CmakeBuilder {
             }
         }
 
+        if target_os() == "android" {
+            cmake_cfg.define("CMAKE_SYSTEM_NAME", "Android");
+
+            let target = target();
+            let proc = target.split('-').find(|_| true).unwrap();
+            match proc {
+                "armv7" => {
+                    cmake_cfg.define("CMAKE_SYSTEM_PROCESSOR", "armv7-a");
+                }
+                "arm" => {
+                    cmake_cfg.define("CMAKE_SYSTEM_PROCESSOR", "armv6");
+                }
+                _ => {
+                    cmake_cfg.define("CMAKE_SYSTEM_PROCESSOR", proc);
+                }
+            }
+        }
+
         if target_vendor() == "apple" && target_os().to_lowercase() == "ios" {
             cmake_cfg.define("CMAKE_SYSTEM_NAME", "iOS");
             if target().ends_with("-ios-sim") || target_arch() == "x86_64" {
@@ -264,7 +289,9 @@ impl crate::Builder for CmakeBuilder {
             }
         }
         if let Some(cmake_cmd) = find_cmake_command() {
-            env::set_var("CMAKE", cmake_cmd);
+            if option_env("CMAKE").is_none() {
+                env::set_var("CMAKE", cmake_cmd);
+            }
         } else {
             eprintln!("Missing dependency: cmake");
             missing_dependency = true;