Set -Werror / /WX via target_compile_options to force warnings as errors

CMakeLists.txt

@@ -165,8 +165,18 @@ if (MSVC)
 
     # Disable Spicy as it is not yet supported in Windows.
     set(DISABLE_SPICY true)
+
+    if (BUILD_WITH_WERROR)
+        # TODO: This is disabled for now because there a bunch of known
+        # compiler warnings on Windows that we don't have good fixes for.
+        #set(WERROR_FLAG "/WX")
+        #set(WERROR_FLAG "/WX")
+    endif ()
 else ()
     include(GNUInstallDirs)
+    if (BUILD_WITH_WERROR)
+        set(WERROR_FLAG "-Werror")
+    endif ()
 endif ()
 
 include(cmake/CommonCMakeConfig.cmake)
@@ -254,6 +264,7 @@ endif ()
 foreach (name zeek_exe zeek_lib zeek_fuzzer_shared)
     if (TARGET ${name})
         target_compile_definitions(${name} PRIVATE ZEEK_CONFIG_SKIP_VERSION_H)
+        target_compile_options(${name} PRIVATE ${WERROR_FLAG})
     endif ()
 endforeach ()
 
@@ -347,6 +358,7 @@ function (zeek_add_subdir_library name)
     add_dependencies(${target_name} zeek_autogen_files)
     target_link_libraries(${target_name} PRIVATE $<BUILD_INTERFACE:zeek_internal>)
     add_clang_tidy_files(${FN_ARGS_SOURCES})
+    target_compile_options(${target_name} PRIVATE ${WERROR_FLAG})
 
     # Take care of compiling BIFs.
     if (FN_ARGS_BIFS)