[MonoVM] support building with Android NDK r22 (#51876)

Context: android/ndk#1427 (comment)

Android NDK r22 changed the tree layout by moving `sysroot` from the NDK
root directory to a subdirectory in the toolchains tree and also by
removing per-platform library/header directories from their previous
location to one under the sysroot above.

MonoVM was built using the CMake's built-in Android NDK support which,
alas, is not compatible with NDK r22 before CMake version 3.19.  It is
therefore better to use the Android CMake toolchain definition script
shipped with the NDK, so that the build works regardless of CMake
version installed on the system.

The r22 toolchain will complain about older CMake versions:

    An old version of CMake is being used that cannot
    automatically detect compiler attributes. Compiler identification is
    being bypassed. Some values may be wrong or missing. Update to CMake
    3.19 or newer to use CMake's built-in compiler identification.

This warning can be safely ignored.

src/mono/mono.proj

@@ -352,13 +352,16 @@
       <_MonoRunInitCompiler>false</_MonoRunInitCompiler>
     </PropertyGroup>
     <ItemGroup Condition="'$(TargetsAndroid)' == 'true'">
-      <_MonoCMakeArgs Include="-DCMAKE_SYSTEM_NAME=Android"/>
-      <_MonoCMakeArgs Include="-DCMAKE_ANDROID_NDK=$(ANDROID_NDK_ROOT)"/>
-      <_MonoCMakeArgs Include="-DCMAKE_SYSTEM_VERSION=$(AndroidApiVersion)"/>
-      <_MonoCMakeArgs Condition="'$(Platform)' == 'arm64'" Include="-DCMAKE_ANDROID_ARCH_ABI=arm64-v8a" />
-      <_MonoCMakeArgs Condition="'$(Platform)' == 'arm'" Include="-DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a" />
-      <_MonoCMakeArgs Condition="'$(Platform)' == 'x86'" Include="-DCMAKE_ANDROID_ARCH_ABI=x86" />
-      <_MonoCMakeArgs Condition="'$(Platform)' == 'x64'" Include="-DCMAKE_ANDROID_ARCH_ABI=x86_64" />
+      <_MonoCMakeArgs Include="-DCMAKE_TOOLCHAIN_FILE=$(ANDROID_NDK_ROOT)/build/cmake/android.toolchain.cmake"/>
+      <_MonoCMakeArgs Include="-DANDROID_NDK=$(ANDROID_NDK_ROOT)"/>
+      <_MonoCMakeArgs Include="-DANDROID_STL=none"/>
+      <_MonoCMakeArgs Include="-DANDROID_CPP_FEATURES=&quot;no-rtti no-exceptions&quot;"/>
+      <_MonoCMakeArgs Include="-DANDROID_NATIVE_API_LEVEL=$(AndroidApiVersion)"/>
+      <_MonoCMakeArgs Include="-DANDROID_PLATFORM=android-$(AndroidApiVersion)"/>
+      <_MonoCMakeArgs Condition="'$(Platform)' == 'arm64'" Include="-DANDROID_ABI=arm64-v8a" />
+      <_MonoCMakeArgs Condition="'$(Platform)' == 'arm'" Include="-DANDROID_ABI=armeabi-v7a" />
+      <_MonoCMakeArgs Condition="'$(Platform)' == 'x86'" Include="-DANDROID_ABI=x86" />
+      <_MonoCMakeArgs Condition="'$(Platform)' == 'x64'" Include="-DANDROID_ABI=x86_64" />
       <_MonoCMakeArgs Include="-DENABLE_MINIMAL=ssa,portability,logging" />
       <_MonoCMakeArgs Include="-DENABLE_SIGALTSTACK=1"/>
       <_MonoCMakeArgs Include="-DDISABLE_CRASH_REPORTING=1"/>
@@ -527,18 +530,27 @@
 
     <!-- Android specific options -->
     <PropertyGroup Condition="'$(TargetsAndroid)' == 'true'">
+      <MonoToolchainPrebuiltOS Condition="$([MSBuild]::IsOSPlatform('Linux'))">linux-x86_64</MonoToolchainPrebuiltOS>
+      <MonoToolchainPrebuiltOS Condition="$([MSBuild]::IsOSPlatform('OSX'))">darwin-x86_64</MonoToolchainPrebuiltOS>
+      <MonoToolchainPrebuiltOS Condition="'$(OS)' == 'Windows_NT'">windows-x86_64</MonoToolchainPrebuiltOS>
+
       <MonoUseCrossTool>true</MonoUseCrossTool>
-      <MonoAOTCMakeSysroot>$(ANDROID_NDK_ROOT)/sysroot</MonoAOTCMakeSysroot>
+      <MonoAotCMakeSysroot Condition="Exists('$(ANDROID_NDK_ROOT)/sysroot')">$(ANDROID_NDK_ROOT)/sysroot</MonoAotCMakeSysroot>
+      <MonoAotCMakeSysroot Condition="'$(MonoAotCMakeSysroot)' == '' And Exists('$(ANDROID_NDK_ROOT)/toolchains/llvm/prebuilt/$(MonoToolchainPrebuiltOS)/sysroot')">$(ANDROID_NDK_ROOT)/toolchains/llvm/prebuilt/$(MonoToolchainPrebuiltOS)/sysroot</MonoAotCMakeSysroot>
       <MonoAotAbi Condition="'$(Platform)' == 'arm64'">aarch64-v8a-linux-android</MonoAotAbi>
       <MonoAotAbi Condition="'$(Platform)' == 'arm'">armv7-none-linux-androideabi</MonoAotAbi>
       <MonoAotAbi Condition="'$(Platform)' == 'x86'">i686-none-linux-android</MonoAotAbi>
       <MonoAotAbi Condition="'$(Platform)' == 'x64'">x86_64-none-linux-android</MonoAotAbi>
       <MonoAotOffsetsFile>$(MonoObjDir)cross/offsets-$(Platform)-android.h</MonoAotOffsetsFile>
     </PropertyGroup>
 
+    <ItemGroup Condition="$([MSBuild]::IsOSPlatform('Linux'))">
+      <_LibClang Include="$(ANDROID_NDK_ROOT)/toolchains/llvm/prebuilt/$(MonoToolchainPrebuiltOS)/lib64/libclang.so.*"/>
+    </ItemGroup>
+
     <PropertyGroup>
       <MonoLibClang Condition="$([MSBuild]::IsOSPlatform('OSX')) and '$(MonoLibClang)' == ''">$(XcodeDir)/Toolchains/XcodeDefault.xctoolchain/usr/lib/libclang.dylib</MonoLibClang>
-      <MonoLibClang Condition="$([MSBuild]::IsOSPlatform('Linux')) and '$(MonoLibClang)' == ''">$(ANDROID_NDK_ROOT)/toolchains/llvm/prebuilt/linux-x86_64/lib64/libclang.so.9svn</MonoLibClang>
+      <MonoLibClang Condition="$([MSBuild]::IsOSPlatform('Linux')) and '$(MonoLibClang)' == ''">@(_LibClang)</MonoLibClang>
       <MonoLibClang Condition="'$(OS)' == 'Windows_NT' and '$(MonoLibClang)' == ''">c:/dev/LLVM/bin/libclang.dll</MonoLibClang>
       <MonoAotCMakeSysroot Condition="'$(MonoAotCMakeSysroot)' == ''">$(MonoCrossDir)</MonoAotCMakeSysroot>
     </PropertyGroup>