run on IOS 11 will crash by run myself builded skia library

[jun chen]

1. I try to build skia library by how to build skia for IOS platform

and I use this command  line: 

'--args=is_debug=true target_cpu="arm64" skia_use_system_expat=false skia_use_system_libjpeg_turbo=false skia_use_system_libpng=false skia_use_system_libwebp=false skia_use_system_zlib=false skia_use_sfntly=false skia_use_freetype=true skia_use_system_freetype2=false skia_use_system_harfbuzz=false skia_pdf_subset_harfbuzz=true skia_use_system_icu=false skia_enable_skottie=true skia_use_metal=true extra_cflags_cc=["-frtti"] target_os="ios"'

2. after skia build success, I test my skia example on  IOS 13 can work normal, But when run on IOS 11, always run crash and output below error:

dyld: Symbol not found: __ZTTNSt3__118basic_stringstreamIcNS_11char_traitsIcEENS_9allocatorIcEEEE

  Referenced from: /var/containers/Bundle/Application/AECCBB3F-E4E1-4D09-A35A-C5D3A3A4F1A6/SkikoSample.app/SkikoSample

  Expected in: /usr/lib/libc++.1.dylib

 in /var/containers/Bundle/Application/AECCBB3F-E4E1-4D09-A35A-C5D3A3A4F1A6/SkikoSample.app/SkikoSample

[jun chen]

1. I' m not sure whether above compile command line correct or not,  please help me hava a look

2. Through the above crash log, on IOS 11 the system libc++ do not have  stringstreamIcNS_1 function,  How do I specify whether to use the system libc++  library or the built-in library when the skia library compile?

[bungeman]

Please see https://bugs.chromium.org/p/skia/issues/detail?id=13967 . It appears that with newer versions of XCode the default minimum has been raised to iOS12. To still run on iOS11 you will need to specify that by adding ios_min_target="11.0" to your args.