message: Android: link to LLVM stl instead of GNU
  The reason for the switch is that LLVM supports futures and promises for
  the architecture armeabi.
diff: @@ -92,36 +92,43 @@ ios_simulator: ios_curl
  android_x86: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=x86)
  android_x86_64: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=x86_64)
  android_mips: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=mips)
  android_mips64: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=mips64)
  android_armeabi: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=armeabi)
  android_armeabi-v7a: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=armeabi-v7a)
  android_arm64-v8a: android_curl
  $(call cmake-build, \
  -DCMAKE_TOOLCHAIN_FILE=$(ANDROID_TOOLCHAIN_CMAKE) \
  + -DANDROID_STL:STRING=c++_static \
  -DANDROID_ABI=arm64-v8a)
  android_curl: android_env_check
  