It seems to break exception handling. (Didn't I remove this earlier?...)
# MacOS: use g++ (which may alias clang++):
#CXX=g++
# MacOS: use g++ (which may alias clang++):
#CXX=g++
-#CXXOPTS=-std=c++11 -Os -Wall -fno-rtti -flto
+#CXXOPTS=-std=c++11 -Os -Wall -flto
#LDFLAGS=-flto
#BUILD_SHUTDOWN=no
#SANITIZEOPTS=-fsanitize=address,undefined
#LDFLAGS=-flto
#BUILD_SHUTDOWN=no
#SANITIZEOPTS=-fsanitize=address,undefined
+# Note: -fno-rtti seems to break exception handling.