Silence unused -Wa argument warning from linking with clang.

CMake automatically forwards all compiler flags to the linker,
and clang doesn't like having -Wa flags being used for linking.

To prevent CMake from doing this would require meddling with the
CMAKE_<LANG>_COMPILE_OBJECT rules, which would get quite messy.

Bug: android/ndk#171
Change-Id: I3295948db64d3459db3af7ba3f0d431689812f80
(cherry picked from commit 78eb716552a0b43c2fc36bebf8ad991e6c77dca9)

android.toolchain.cmake

@@ -528,6 +528,14 @@ else()
 	list(APPEND ANDROID_LINKER_FLAGS
 		-Wl,-z,noexecstack)
 endif()
+if(ANDROID_TOOLCHAIN STREQUAL clang)
+	# CMake automatically forwards all compiler flags to the linker,
+	# and clang doesn't like having -Wa flags being used for linking.
+	# To prevent CMake from doing this would require meddling with
+	# the CMAKE_<LANG>_COMPILE_OBJECT rules, which would get quite messy.
+	list(APPEND ANDROID_LINKER_FLAGS
+		-Qunused-arguments)
+endif()
 if(ANDROID_DISABLE_RELRO)
 	list(APPEND ANDROID_LINKER_FLAGS
 		-Wl,-z,norelro -Wl,-z,lazy)

test/CMakeLists.txt

@@ -4,6 +4,9 @@ cmake_minimum_required(VERSION 3.6.0)
 if(CMAKE_NINJA_FORCE_RESPONSE_FILE)
 endif()
 
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
+
 add_library(c_shared SHARED shared/shared.c)
 add_library(c_static STATIC static/static.c)
 set(C_LIBRARIES c_shared c_static)