[Zorg] Explicitly use `-stdlib=libstdc++` for Android.

[danalbert]

Summary

This builder uses an old version of the NDK with a just-built version
of the Clang. This builder is making use of an NDK standalone
toolchain. For older NDKs, these toolchins have the C++ stdlib headers
and libraries installed to the GNU stdlib paths.

This causes an issue when I try to update the default -stdlib for
Android targets in Clang as this builder will begin looking in the
libc++ paths when it does not have an STL available at that path.

Explicitly use -stdlib=libstdc++ to keep the old tools working with
a new Clang until this builder is using an NDK new enough to not need
it (NDK r19).

[eugenis]

LGTM

zorg/trunk/zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

 
 function configure_android { # ARCH triple
   local _arch=$1
   local _triple=$2
 
   local ANDROID_TOOLCHAIN=$ROOT/android_ndk/standalone-$_arch
   local ANDROID_LIBRARY_OUTPUT_DIR=$(ls -d $ROOT/llvm_build64/lib/clang/* | tail -1)
   local ANDROID_EXEC_OUTPUT_DIR=$ROOT/llvm_build64/bin
-  local ANDROID_FLAGS="--target=$_triple --sysroot=$ANDROID_TOOLCHAIN/sysroot -B$ANDROID_TOOLCHAIN"
+  local ANDROID_FLAGS="--target=$_triple -stdlib=libstdc++ --sysroot=$ANDROID_TOOLCHAIN/sysroot -B$ANDROID_TOOLCHAIN"
 
   # Always clobber android build tree.
   # It has a hidden dependency on clang (through CXX) which is not known to
   # the build system.
   rm -rf compiler_rt_build_android_$_arch
   mkdir -p compiler_rt_build_android_$_arch
   rm -rf llvm_build_android_$_arch
   mkdir -p llvm_build_android_$_arch