Remove warnings-as-errors by default

Compiling C++ on various different platforms with as many out of tree
dependencies as we have is volatile at best.
In order to prevent a third party warning from ruining the build for
people who don't care about third party warnings, we remove
warnings-as-errors by default.
They are still enabled by default on CI.

advancedSettings.pro

@@ -123,3 +123,7 @@ debugSymbolsAndLogs {
     CONFIG += force_debug_info
     DEFINES += ENABLE_DEBUG_LOGGING
 }
+
+warnings_as_errors {
+    message(Warnings as errors enabled.)
+}