cmake: Add WERROR option

Author: hebasto

CMakeLists.txt

@@ -55,6 +55,7 @@ cmake_dependent_option(CXX20 "Enable compilation in C++20 mode." OFF "NOT MSVC"
 option(THREADLOCAL "Enable features that depend on the C++ thread_local keyword (currently just thread names in debug logs)." ON)
 option(HARDENING "Attempt to harden the resulting executables." ON)
 option(REDUCE_EXPORTS "Attempt to reduce exported symbols in the resulting executables." OFF)
+option(WERROR "Treat compiler warnings as errors." OFF)
 
 tristate_option(CCACHE "Use ccache for compiling." "if ccache is found." AUTO)
 tristate_option(WITH_NATPMP "Enable NAT-PMP." "if libnatpmp is found." AUTO)
@@ -296,6 +297,19 @@ if(REDUCE_EXPORTS)
   try_append_linker_flag("-Wl,--exclude-libs,ALL" TARGET core)
 endif()
 
+if(WERROR)
+  if(MSVC)
+    set(werror_flag "/WX")
+  else()
+    set(werror_flag "-Werror")
+  endif()
+  try_append_cxx_flags(${werror_flag} TARGET core RESULT_VAR compiler_supports_werror)
+  if(NOT compiler_supports_werror)
+    message(FATAL_ERROR "WERROR set but ${werror_flag} is not usable.")
+  endif()
+  unset(werror_flag)
+endif()
+
 find_package(Python3 3.9 COMPONENTS Interpreter)
 set(PYTHON_COMMAND ${Python3_EXECUTABLE})
 
@@ -352,6 +366,7 @@ message("Linker flags for shared libraries ..... ${CMAKE_SHARED_LINKER_FLAGS}")
 print_config_flags()
 message("Use assembly routines ................. ${ASM}")
 message("Attempt to harden executables ......... ${HARDENING}")
+message("Treat compiler warnings as errors ..... ${WERROR}")
 message("Use ccache for compiling .............. ${CCACHE}")
 message("\n")
 if(configure_warnings)