Android: Add options to control exceptions/rtti

With the NDK's `android.toolchain.cmake`, the user can control whether
exceptions/rtti is enabled using `ANDROID_CPP_FEATURES`:

  https://android.googlesource.com/platform/ndk/+/43b2de34ef9e3a70573fe51a9e069f985a4be5b9/build/cmake/android.toolchain.cmake#548

Add `CMAKE_ANDROID_RTTI` and `CMAKE_ANDROID_EXCEPTIONS` to support that.

Help/manual/cmake-variables.7.rst

@@ -336,6 +336,7 @@ Variables that Control the Build
    /variable/CMAKE_ANDROID_ARM_MODE
    /variable/CMAKE_ANDROID_ARM_NEON
    /variable/CMAKE_ANDROID_ASSETS_DIRECTORIES
+   /variable/CMAKE_ANDROID_EXCEPTIONS
    /variable/CMAKE_ANDROID_GUI
    /variable/CMAKE_ANDROID_JAR_DEPENDENCIES
    /variable/CMAKE_ANDROID_JAR_DIRECTORIES
@@ -349,6 +350,7 @@ Variables that Control the Build
    /variable/CMAKE_ANDROID_PROCESS_MAX
    /variable/CMAKE_ANDROID_PROGUARD
    /variable/CMAKE_ANDROID_PROGUARD_CONFIG_PATH
+   /variable/CMAKE_ANDROID_RTTI
    /variable/CMAKE_ANDROID_SECURE_PROPS_PATH
    /variable/CMAKE_ANDROID_SKIP_ANT_STEP
    /variable/CMAKE_ANDROID_STANDALONE_TOOLCHAIN

Help/variable/CMAKE_ANDROID_EXCEPTIONS.rst

@@ -0,0 +1,7 @@
+CMAKE_ANDROID_EXCEPTIONS
+------------------------
+
+.. versionadded:: 3.20
+
+When :ref:`Cross Compiling for Android with the NDK`, this variable may be set
+to specify whether exceptions are enabled.

Help/variable/CMAKE_ANDROID_RTTI.rst

@@ -0,0 +1,7 @@
+CMAKE_ANDROID_RTTI
+------------------
+
+.. versionadded:: 3.20
+
+When :ref:`Cross Compiling for Android with the NDK`, this variable may be set
+to specify whether RTTI is enabled.

Modules/Platform/Android-Common.cmake

@@ -81,6 +81,12 @@ if(CMAKE_ANDROID_STL_TYPE)
         "Android: STL '${CMAKE_ANDROID_STL_TYPE}' not supported by this NDK."
         )
     endif()
+    if(DEFINED CMAKE_ANDROID_RTTI)
+      set(_ANDROID_STL_RTTI ${CMAKE_ANDROID_RTTI})
+    endif()
+    if(DEFINED CMAKE_ANDROID_EXCEPTIONS)
+      set(_ANDROID_STL_EXCEPTIONS ${CMAKE_ANDROID_EXCEPTIONS})
+    endif()
   elseif(CMAKE_ANDROID_NDK)
 
     macro(__android_stl_inc lang dir req)