Build issue on Debian - `.travis/deps.sh linux` doesn't ensure C++ is installed

[rbanffy]

Staring from clean Debian container image (docker.io/library/debian:latest), and setting up the environment with the following commands:

apt install git sudo
git clone https://github.com/open-simh/simh.git
cd simh
.travis/deps.sh linux

When attempting a build with either unix or ninja flavors, the build process fails as follows:

root@efcd54277366:/simh# cmake/cmake-builder.sh --flavor unix 
** cmake version 3.31.6

CMake suite maintained and supported by Kitware (kitware.com/cmake).
cmake/cmake-builder.sh: SIMH top-evel directory: /simh
cmake/cmake-builder.sh: Build directory:         /simh/cmake/build-unix
cmake/cmake-builder.sh: Removing CMakeCache.txt and CMakeFiles
/usr/bin/cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release -S /simh -B /simh/cmake/build-unix 
-- CMAKE_MODULE_PATH: /simh/cmake;/simh/cmake/installer-customizations
-- The C compiler identification is GNU 14.2.0
-- The CXX compiler identification is unknown
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
CMake Error at CMakeLists.txt:83 (project):
  No CMAKE_CXX_COMPILER could be found.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.


-- Configuring incomplete, errors occurred!
*** cmake/cmake-builder.sh: Errors detected during environment generation. Exiting.

and

root@efcd54277366:/simh# cmake/cmake-builder.sh --flavor ninja
** cmake version 3.31.6

CMake suite maintained and supported by Kitware (kitware.com/cmake).
cmake/cmake-builder.sh: SIMH top-evel directory: /simh
cmake/cmake-builder.sh: Build directory:         /simh/cmake/build-ninja
cmake/cmake-builder.sh: Removing CMakeCache.txt and CMakeFiles
/usr/bin/cmake -G "Ninja" -DCMAKE_BUILD_TYPE=Release -S /simh -B /simh/cmake/build-ninja 
-- CMAKE_MODULE_PATH: /simh/cmake;/simh/cmake/installer-customizations
-- The C compiler identification is GNU 14.2.0
-- The CXX compiler identification is unknown
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
CMake Error at CMakeLists.txt:83 (project):
  No CMAKE_CXX_COMPILER could be found.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.


-- Configuring incomplete, errors occurred!
*** cmake/cmake-builder.sh: Errors detected during environment generation. Exiting.

Adding g++ to the packages in the install_linux function resolves the issue. Should we add the right compilers to the other Unix setups as well? I'm not sure whether it's possible to have a MacPorts or Homebrew install without a C++ compiler (it comes with Xcode, which is a requirement), but the Arch Linux setup doesn't mention it either (on Debian, C is installed with the other requirements, but C++ isn't).