Set default ndk version to 21.

[oontvoo]

Summary

The compiler-rt/test/lit.common.cfg.py (around line 68) decides to use libstdc++ if the ndk version is older than 18.

[vitalybuka]

compiler-rt/CMakeLists.txt

127

we should use cmake -DANDROID_NDK_VERSION= with a real version

@pcc D57733 looks like a temporarily workaround. After we switch the bot past 19 we should remove ANDROID_NDK_VERSION and android_ndk_version from the code.

[pcc]

compiler-rt/CMakeLists.txt

127

Yes, once we start requiring NDK >= r19 we should be able to remove this.

[oontvoo]

compiler-rt/CMakeLists.txt

127

we should use cmake -DANDROID_NDK_VERSION= with a real version

@pcc D57733 looks like a temporarily workaround. After we switch the bot past 19 we should remove ANDROID_NDK_VERSION and android_ndk_version from the code.

Ok, so it's chicken-n-egg? Do we want to switch the bot first? or update this first?

[oontvoo]

updated

[oontvoo]

This is no longer needed, because we just use -DANDROID_NDK_VERSION

compiler-rt/CMakeLists.txt

if (${COMPILER_RT_DEFAULT_TARGET_ARCH} MATCHES "^arm")
     CHECK_SYMBOL_EXISTS (__thumb__ "" COMPILER_RT_ARM_THUMB)
   endif()
 endif()
 if ("${COMPILER_RT_DEFAULT_TARGET_TRIPLE}" MATCHES ".*android.*")
   set(ANDROID 1)
 endif()
 pythonize_bool(ANDROID)
 
-set(ANDROID_NDK_VERSION 18
+set(ANDROID_NDK_VERSION 21
     CACHE STRING "Set this to the Android NDK version that you are using")
 
 set(COMPILER_RT_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(COMPILER_RT_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 
 pythonize_bool(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
 
 # We support running instrumented tests when we're not cross compiling

compiler-rt/test/lit.common.cfg.py

if config.android:
   # Prepend the flag so that it can be overridden.
   config.target_cflags = "-pie -fuse-ld=gold " + config.target_cflags
   if config.android_ndk_version < 19:
     # With a new compiler and NDK < r19 this flag ends up meaning "link against
     # libc++", but NDK r19 makes this mean "link against the stub libstdc++ that
     # just contains a handful of ABI functions", which makes most C++ code fail
     # to link. In r19 and later we just use the default which is libc++.
     config.cxx_mode_flags.append('-stdlib=libstdc++')
+  else
+    config.cxx_mode_flags.append('-stdlib=libc++')
 
 config.environment = dict(os.environ)
 
 # Clear some environment variables that might affect Clang.
 possibly_dangerous_env_vars = ['ASAN_OPTIONS', 'DFSAN_OPTIONS', 'LSAN_OPTIONS',
                                'MSAN_OPTIONS', 'UBSAN_OPTIONS',
                                'COMPILER_PATH', 'RC_DEBUG_OPTIONS',
                                'CINDEXTEST_PREAMBLE_FILE', 'LIBRARY_PATH',