[build,c++] add CXXCompilerFlags to set warnings

Just like with the C components and CompilerFlags.cmake add a
configuration for C++ that disables specific warnings only found in C++
code.

cmake/CXXCompilerFlags.cmake

@@ -0,0 +1,60 @@
+include(CheckCXXCompilerFlag)
+
+macro (checkCXXFlag FLAG)
+	check_cxx_compiler_flag("${FLAG}" CXXFLAG${FLAG})
+	if(CXXFLAG${FLAG})
+		string(APPEND CMAKE_CXX_FLAGS " ${FLAG}")
+	else()
+		message(WARNING "compiler does not support ${FLAG}")
+	endif()
+endmacro()
+
+option(ENABLE_WARNING_VERBOSE "enable -Weveryting (and some exceptions) for compile" ON)
+option(ENABLE_WARNING_ERROR "enable -Werror for compile" OFF)
+
+if (ENABLE_WARNING_VERBOSE)
+	if (MSVC)
+		# Remove previous warning definitions,
+		# NMake is otherwise complaining.
+		foreach (flags_var_to_scrub
+			CMAKE_CXX_FLAGS
+			CMAKE_CXX_FLAGS_DEBUG
+			CMAKE_CXX_FLAGS_RELEASE
+			CMAKE_CXX_FLAGS_RELWITHDEBINFO
+			CMAKE_CXX_FLAGS_MINSIZEREL)
+			string (REGEX REPLACE "(^| )[/-]W[ ]*[1-9]" " "
+			"${flags_var_to_scrub}" "${${flags_var_to_scrub}}")
+		endforeach()
+
+		set(C_WARNING_FLAGS
+			/W4
+			/wo4324
+		)
+	else()
+		set(C_WARNING_FLAGS
+			-Weverything
+			-Wall
+			-Wpedantic
+			-Wno-padded
+			-Wno-switch-enum
+			-Wno-cast-align
+			-Wno-declaration-after-statement
+			-Wno-unsafe-buffer-usage
+			-Wno-reserved-identifier
+			-Wno-covered-switch-default
+			-Wno-ctad-maybe-unsupported
+		)
+	endif()
+
+	foreach(FLAG ${C_WARNING_FLAGS})
+		CheckCXXFlag(${FLAG})
+	endforeach()
+endif()
+
+
+if (ENABLE_WARNING_ERROR)
+	CheckCXXFlag(-Werror)
+endif()
+
+set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} CACHE STRING "default CXXFLAGS")
+message("Using CXXFLAGS ${CMAKE_CXX_FLAGS}")