Fix CFLAGS and CXXFLAGS when coverage enabled.

Author: mtl1979

CMakeLists.txt

@@ -47,6 +47,11 @@ include(CMakeDependentOption)
 include(CMakePackageConfigHelpers)
 include(FeatureSummary)
 
+# We need to enable C++ before trying to check for coverage
+if(WITH_GTEST OR WITH_BENCHMARKS)
+  enable_language(CXX)
+endif()
+
 include(cmake/detect-arch.cmake)
 include(cmake/detect-install-dirs.cmake)
 include(cmake/detect-coverage.cmake)