Fix Android builds

For starters, they should link against libc++, as they have always
intended to use STL "c++_shared".

https://github.com/Kitware/CMake/blob/824f2a7a200f9d3e41a2b68be2d5e1cc678afffa/Modules/Platform/Android-Common.cmake#L70-L75

Also, fix the variable names we define, as far as I know cmake never
cared about ANDROID_NATIVE_API_LEVEL nor ANDROID_STL.

Author: nox

boring-sys/build/config.rs

@@ -10,6 +10,7 @@ pub(crate) struct Config {
     pub(crate) target: String,
     pub(crate) target_arch: String,
     pub(crate) target_os: String,
+    pub(crate) unix: bool,
     pub(crate) features: Features,
     pub(crate) env: Env,
 }
@@ -46,6 +47,7 @@ impl Config {
         let target = env::var("TARGET").unwrap();
         let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
         let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
+        let unix = env::var("CARGO_CFG_UNIX").is_ok();
 
         let features = Features::from_env();
         let env = Env::from_env(&host, &target, features.is_fips_like());
@@ -63,6 +65,7 @@ impl Config {
             target,
             target_arch,
             target_os,
+            unix,
             features,
             env,
         };

boring-sys/build/main.rs

@@ -262,8 +262,8 @@ fn get_boringssl_cmake_config(config: &Config) -> cmake::Config {
             boringssl_cmake.define("CMAKE_TOOLCHAIN_FILE", toolchain_file);
 
             // 21 is the minimum level tested. You can give higher value.
-            boringssl_cmake.define("ANDROID_NATIVE_API_LEVEL", "21");
-            boringssl_cmake.define("ANDROID_STL", "c++_shared");
+            boringssl_cmake.define("CMAKE_SYSTEM_VERSION", "21");
+            boringssl_cmake.define("CMAKE_ANDROID_STL_TYPE", "c++_shared");
         }
 
         "macos" => {
@@ -561,14 +561,11 @@ fn get_cpp_runtime_lib(config: &Config) -> Option<String> {
         return cpp_lib.clone().into_string().ok();
     }
 
-    // TODO(rmehra): figure out how to do this for windows
-    if env::var_os("CARGO_CFG_UNIX").is_some() {
-        match env::var("CARGO_CFG_TARGET_OS").unwrap().as_ref() {
-            "macos" | "ios" | "freebsd" => Some("c++".into()),
-            _ => Some("stdc++".into()),
-        }
-    } else {
-        None
+    match &*config.target_os {
+        "macos" | "ios" | "freebsd" | "android " => Some("c++".into()),
+        _ if config.unix => Some("stdc++".into()),
+        // TODO(rmehra): figure out how to do this for windows
+        _ => None,
     }
 }