build: add a workaround for Android builds

The android build requires linking to libunwind to prevent underlinking.
This library is squirreled away into the compiler resource directory and
since we do not use the NDK compiler we do not pick it up. Explicitly
add the directory to our linker search path to pick up the necessary
library. This library should really be provided by the NDK as we cannot
ascertain if the unwinder has been modified or contains extensions.

CMakeLists.txt

@@ -33,6 +33,26 @@ target_include_directories(firebase INTERFACE
 if(ANDROID)
   target_link_directories(firebase INTERFACE
     third_party/firebase-development/usr/libs/android/${CMAKE_ANDROID_ARCH_ABI})
+
+  # Add the compiler resource directory as a library search path explicitly as
+  # we do not use `clang` from the NDK but do require `libunwind.a` which is not
+  # in the sysroot (platform SDK) but rather placed into the resource directory
+  # on the Android platform.
+  if(CMAKE_ANDROID_ARCH STREQUAL arm64)
+    target_link_directories(firebase INTERFACE
+      $ENV{ANDROID_NDK_ROOT}/toolchains/llvm/prebuilt/windows-x86_64/lib/clang/17/lib/linux/aarch64)
+  elseif(CMAKE_ANDROID_ARCH STREQUAL arm)
+    target_link_directories(firebase INTERFACE
+      $ENV{ANDROID_NDK_ROOT}/toolchains/llvm/prebuilt/windows-x86_64/lib/clang/17/lib/linux/arm)
+  elseif(CMAKE_ANDROID_ARCH STREQUAL x86)
+    target_link_directories(firebase INTERFACE
+      $ENV{ANDROID_NDK_ROOT}/toolchains/llvm/prebuilt/windows-x86_64/lib/clang/17/lib/linux/i386)
+  elseif(CMAKE_ANDROID_ARCH STREQUAL x86_64)
+    target_link_directories(firebase INTERFACE
+      $ENV{ANDROID_NDK_ROOT}/toolchains/llvm/prebuilt/windows-x86_64/lib/clang/17/lib/linux/x86_64)
+  else()
+    message(SEND_ERROR "unsupported architecture for Android")
+  endif()
 elseif(WIN32)
   target_link_directories(firebase INTERFACE
     third_party/firebase-development/usr/libs/windows