Set project as C project in CMakeLists.txt

The openscap tool has been recently integrated in the buildroot build
system ([1]), which makes the openscap tool buildable for a wide variety
or architectures/OSes, with a wide variety of _compilers_. And so when
such compilers are not supporting C++ projects (as it is the case with a
default buildroot toolchain), the build breaks on the following error
(see [2] for an example):

  -- Detecting CXX compiler ABI info
  -- Detecting CXX compiler ABI info - failed
  -- Check for working CXX compiler: /bin/false
  -- Check for working CXX compiler: /bin/false - broken
  CMake Error at /usr/share/cmake/Modules/CMakeTestCXXCompiler.cmake:73 (message):
    The C++ compiler

      "/bin/false"

    is not able to compile a simple test program.

    It fails with the following output:

      Change Dir: '/home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI'

      Run Build Command(s): /usr/bin/cmake -E env VERBOSE=1 /usr/bin/make -f Makefile cmTC_1834b/fast
      make[1]: Entering directory '/home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI'
      /usr/bin/make  -f CMakeFiles/cmTC_1834b.dir/build.make CMakeFiles/cmTC_1834b.dir/build
      make[2]: Entering directory '/home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI'
      Building CXX object CMakeFiles/cmTC_1834b.dir/testCXXCompiler.cxx.o
      /bin/false    -o CMakeFiles/cmTC_1834b.dir/testCXXCompiler.cxx.o -c /home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI/testCXXCompiler.cxx
      make[2]: *** [CMakeFiles/cmTC_1834b.dir/build.make:81: CMakeFiles/cmTC_1834b.dir/testCXXCompiler.cxx.o] Error 1
      make[2]: Leaving directory '/home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI'
      make[1]: *** [Makefile:134: cmTC_1834b/fast] Error 2
      make[1]: Leaving directory '/home/autobuild/autobuild/instance-6/output-1/build/openscap-1.3.12/buildroot-build/CMakeFiles/CMakeScratch/TryCompile-tUydqI'

    CMake will not be able to correctly generate this project.
  Call Stack (most recent call first):
    CMakeLists.txt:11 (project)

openscap does not have any C++ code to build, so restricting builds to
toolchains supporting C++ is overconstraining, the configuration step
should rather not try to check C++ support.

Enforce the project as a C project in CMakeLists.txt to make sure not to
test C++ features on the used toolchain.

[1] https://buildroot.org/
[2] https://autobuild.buildroot.org/results/1fe550ffa79f0a083a450ae03fe067a8ab7336be/build-end.log

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>

Author: Tropicao

CMakeLists.txt

@@ -8,7 +8,7 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
 		"MinSizeRel" "RelWithDebInfo")
 endif()
 
-project("openscap")
+project("openscap" C)
 set(OPENSCAP_VERSION_MAJOR "1")
 set(OPENSCAP_VERSION_MINOR "4")
 set(OPENSCAP_VERSION_PATCH "4")