ZStandard: Use flags from absl

[oshogbo]

I'm not sure how this change happened as in my code it was pointing to the right header.

We can't use here the one from sapi as there is a conflict in the headers:

[9/10] Building CXX object example/CMakeFiles/sapi_minizstd.dir/main.cc.o
In file included from _deps/absl-src/absl/flags/internal/parse.h:23,
                 from _deps/absl-src/absl/flags/parse.h:29,
                 from /home/oshogbo/sapi-zstd/contrib/zstd/sandboxed.h:25,
                 from ../example/main.cc:24:
_deps/absl-src/absl/flags/declare.h:63: warning: "ABSL_DECLARE_FLAG" redefined
   63 | #define ABSL_DECLARE_FLAG(type, name)                        \
      | 
In file included from /home/oshogbo/sapi-zstd/contrib/zstd/sandboxed.h:24,
                 from ../example/main.cc:24:
/home/oshogbo/sapi-zstd/sandboxed_api/util/flag.h:23: note: this is the location of the previous definition
   23 | #define ABSL_DECLARE_FLAG(type, name) DECLARE_##type(name)
      | 

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This change is 

[oshogbo]

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contrib/zstd/sandboxed.h, line 24 at r1 (raw file):

Previously, okunz (Oliver Kunz) wrote…

This header file doesn't use absl::Flags, I'm assuming you're referring to example/main.cc:60? Google's C++ style doesn't rely on transitive inclusions, see https://google.github.io/styleguide/cppguide.html#Include_What_You_Use

I mean I'm happy to move it but in different PR I was asked to move it here: https://reviewable.io/reviews/google/sandboxed-api/100#-MutldPd4TWOT713MUEz