Dockerfile fails when run on git repository without submodules initialized

[vanhauser-thc]

something broke the Dockerfile:

# docker build -t symcc .
[...]
-- Detecting CXX compile features - done
-- Could NOT find Z3 (missing: Z3_DIR)
-- Configuring done
CMake Error at qsym_backend/CMakeLists.txt:58 (add_library):
  Cannot find source file:

    qsym/qsym/pintool/expr_cache.cpp

  Tried extensions .c .C .c++ .cc .cpp .cxx .cu .m .M .mm .h .hh .h++ .hm
  .hpp .hxx .in .txx

CMake Error at qsym_backend/CMakeLists.txt:58 (add_library):
  No SOURCES given to target: SymRuntime

CMake Generate step failed.  Build files cannot be regenerated correctly.
[6/14] Building CXX object CMakeFiles/Symbolize.dir/compiler/Main.cpp.o
[7/14] Building CXX object CMakeFiles/Symbolize.dir/compiler/Runtime.cpp.o
[8/14] Building CXX object CMakeFiles/Symbolize.dir/compiler/Pass.cpp.o
[9/14] Building CXX object CMakeFiles/Symbolize.dir/compiler/Symbolizer.cpp.o
ninja: build stopped: subcommand failed.
The command '/bin/sh -c cmake -G Ninja         -DQSYM_BACKEND=ON         -DCMAKE_BUILD_TYPE=RelWithDebInfo         -DZ3_TRUST_SYSTEM_VERSION=on         /symcc_source     && ninja check     && cargo install --path /symcc_source/util/symcc_fuzzing_helper' returned a non-zero code: 1

[aurelf]

I could reproduce this when not running "git submodule init / update" before launching docker, as described in the documentation. But I imagine that this could be automated... I'll mark this as possible enhancement.