cmake: Only enable CXX when running the coverage

Commit 25a678190c introduced code coverage
collection. That also introduced a dependency to CXX language.

When cross-compiling libssh in an environment that doesn't have a C++ compiler
the following error is raised: "No CMAKE_CXX_COMPILER could be found.".

Since the C++ part is only needed for the coverage part, this commit only enable
that language dependency when actually needing it.

Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

CMakeLists.txt

@@ -9,7 +9,7 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules")
 include(DefineCMakeDefaults)
 include(DefineCompilerFlags)
 
-project(libssh VERSION 0.11.00 LANGUAGES C CXX)
+project(libssh VERSION 0.11.00 LANGUAGES C)
 
 # global needed variable
 set(APPLICATION_NAME ${PROJECT_NAME})
@@ -190,6 +190,7 @@ endif (WITH_SYMBOL_VERSIONING AND ABIMAP_FOUND)
 
 # Coverage
 if (WITH_COVERAGE)
+    ENABLE_LANGUAGE(CXX)
     include(CodeCoverage)
     setup_target_for_coverage_lcov(
         NAME "coverage"

cmake/Modules/AddCMockaTest.cmake

@@ -117,6 +117,7 @@ function(ADD_CMOCKA_TEST _TARGET_NAME)
         ${TARGET_SYSTEM_EMULATOR} ${_TARGET_NAME}
     )
     if (WITH_COVERAGE)
+        ENABLE_LANGUAGE(CXX)
         include(CodeCoverage)
         append_coverage_compiler_flags_to_target(${_TARGET_NAME})
     endif (WITH_COVERAGE)