[presets] Escalate C++ "unused" warnings in macOS smoke test

Author: AnthonyLatsis

CMakeLists.txt

@@ -1,5 +1,7 @@
 cmake_minimum_required(VERSION 3.19.6)
 
+# Pull in any Swift-only C++ flags.
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${SWIFT_CXX_FLAGS}")
 
 #  set_property(GLOBAL PROPERTY GLOBAL_DEPENDS_DEBUG_MODE 1)
 

utils/build-presets.ini

@@ -671,6 +671,10 @@ skip-test-llbuild
 
 enable-new-runtime-build
 
+# Escalate certain C++ warnings to errors for Swift.
+extra-cmake-options=
+   -DSWIFT_CXX_FLAGS="-Werror=unused"
+
 [preset: buildbot_incremental,tools=RA,stdlib=RD,smoketest=macosx,flto]
 mixin-preset=buildbot_incremental,tools=RA,stdlib=RD,smoketest=macosx
 build-subdir=buildbot_incremental