63cb882 introduced a hotfix into .NET 9 to allow for building with NDK 27. This causes build to fail when using old NDK 23 locally:

  Libclang '~/android-ndk-r23c/toolchains/llvm/prebuilt/linux-x86_64/lib64/libclang.so.12git /usr/local/lib/libclang.so' doesn't exist.

Error stems form incorrect conditions in mono.proj. _LibClang is an item not a property, it should be referred to using @.

Reproduction steps:

export SDK
export NDK 23
./build.sh -arch x64 -s mono+libs+libs.tests -os android  -c Release

\cc: @steveisok