[compiler-rt] Improve defaults for Android

[smeenai]

Summary

Android has only used libc++ for a long time, and since NDK r23, it
also always uses compiler-rt and LLVM's libunwind (which is linked
statically). Reflect these defaults in compiler-rt's build, instead of
requiring the correct settings to always be externally specified.

[srhines]

Thanks for making this better.

compiler-rt/CMakeLists.txt

macro(handle_default_cxx_lib var)
   # Specifying -stdlib= in CMAKE_CXX_FLAGS overrides the defaults.
   if (CMAKE_CXX_FLAGS MATCHES "-stdlib=([a-zA-Z+]*)")
     set(${var}_LIBNAME "${CMAKE_MATCH_1}")
     set(${var}_SYSTEM 1)
   elseif (${var} STREQUAL "default")
     if (APPLE OR CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
       set(${var}_LIBNAME "libc++")
       set(${var}_SYSTEM 1)
-    elseif (FUCHSIA)
+    elseif (ANDROID OR FUCHSIA)
       set(${var}_LIBNAME "libc++")
       set(${var}_INTREE 1)
     else()
       set(${var}_LIBNAME "libstdc++")
       set(${var}_SYSTEM 1)
     endif()
   else()
     set(${var}_LIBNAME "${${var}}")

 # This needs to be a full C++ library for linking gtest and unit tests.
 # TODO: Mark this as internal flag, most users should use COMPILER_RT_CXX_LIBRARY.
 set(SANITIZER_TEST_CXX "default" CACHE STRING
     "Specify C++ library to use for tests.")
 set(CXXLIBS none default libstdc++ libc++)
 set_property(CACHE SANITIZER_TEST_CXX PROPERTY STRINGS ;${CXXLIBS})
 handle_default_cxx_lib(SANITIZER_TEST_CXX)
 
-option(COMPILER_RT_USE_LLVM_UNWINDER "Use the LLVM unwinder." OFF)
+set(DEFAULT_COMPILER_RT_USE_LLVM_UNWINDER OFF)
+if (ANDROID)
+  set(DEFAULT_COMPILER_RT_USE_LLVM_UNWINDER ON)
+endif()
+
+option(COMPILER_RT_USE_LLVM_UNWINDER
+  "Use the LLVM unwinder." ${DEFAULT_COMPILER_RT_USE_LLVM_UNWINDER})
 cmake_dependent_option(COMPILER_RT_ENABLE_STATIC_UNWINDER
   "Statically link the LLVM unwinder." OFF
   "COMPILER_RT_USE_LLVM_UNWINDER" OFF)
 
 set(DEFAULT_SANITIZER_USE_STATIC_LLVM_UNWINDER OFF)
-if (FUCHSIA)
+if (ANDROID OR FUCHSIA)
   set(DEFAULT_SANITIZER_USE_STATIC_LLVM_UNWINDER ON)
 elseif (DEFINED LIBUNWIND_ENABLE_SHARED AND NOT LIBUNWIND_ENABLE_SHARED)
   set(DEFAULT_SANITIZER_USE_STATIC_LLVM_UNWINDER ON)
 endif()
 
 option(SANITIZER_USE_STATIC_LLVM_UNWINDER
   "Use static LLVM unwinder." ${DEFAULT_SANITIZER_USE_STATIC_LLVM_UNWINDER})
 pythonize_bool(SANITIZER_USE_STATIC_LLVM_UNWINDER)

 if (NOT "${COMPILER_RT_CXX_LIBRARY}" IN_LIST COMPILER_RT_SUPPORTED_CXX_LIBRARIES)
   message(FATAL_ERROR "Unsupported C++ library: '${COMPILER_RT_CXX_LIBRARY}'. Supported values are ${COMPILER_RT_SUPPORTED_CXX_LIBRARIES}.")
 endif()
 cmake_dependent_option(COMPILER_RT_STATIC_CXX_LIBRARY
   "Statically link the C++ library." OFF
   "COMPILER_RT_CXX_LIBRARY" OFF)
 
 set(DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY OFF)
-if (FUCHSIA)
+if (ANDROID OR FUCHSIA)
   set(DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY ON)
 endif()
 
 option(COMPILER_RT_USE_BUILTINS_LIBRARY
   "Use compiler-rt builtins instead of libgcc" ${DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY})
 
 include(config-ix)