[android] Link with static C++ ABI for Android.

Normally, the C++ shared library would have link against the C++ ABI
shared library, but the Android NDK does not distribute the later, so
one need to link manually against the static C++ ABI from the NDK.

Author: drodriguez

cmake/modules/AddSwift.cmake

@@ -434,12 +434,14 @@ function(_add_variant_link_flags)
     # we need to add the math library, which is linked implicitly by libc++.
     list(APPEND result "-nostdlib++" "-lm")
     if("${LFLAGS_ARCH}" MATCHES armv7)
-      list(APPEND result "${SWIFT_ANDROID_NDK_PATH}/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_shared.so")
+      set(android_libcxx_path "${SWIFT_ANDROID_NDK_PATH}/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a")
     elseif("${LFLAGS_ARCH}" MATCHES aarch64)
-      list(APPEND result "${SWIFT_ANDROID_NDK_PATH}/sources/cxx-stl/llvm-libc++/libs/arm64-v8a/libc++_shared.so")
+      set(android_libcxx_path "${SWIFT_ANDROID_NDK_PATH}/sources/cxx-stl/llvm-libc++/libs/arm64-v8a")
     else()
       message(SEND_ERROR "unknown architecture (${LFLAGS_ARCH}) for android")
     endif()
+    list(APPEND link_libraries "${android_libcxx_path}/libc++abi.a")
+    list(APPEND link_libraries "${android_libcxx_path}/libc++_shared.so")
     swift_android_lib_for_arch(${LFLAGS_ARCH} ${LFLAGS_ARCH}_LIB)
     foreach(path IN LISTS ${LFLAGS_ARCH}_LIB)
       list(APPEND library_search_directories ${path})