Makefile: Use preview-overflow flag by default

-D compiler_rt is not needed in all platforms actually but trying to keep configuration simpler

Makefile

@@ -27,7 +27,7 @@ static ?=       ## Enable static linking
 O := .build
 SOURCES := $(shell find src -name '*.cr')
 SPEC_SOURCES := $(shell find spec -name '*.cr')
-override FLAGS += $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )
+override FLAGS += -D preview_overflow -D compiler_rt $(if $(release),--release )$(if $(stats),--stats )$(if $(progress),--progress )$(if $(threads),--threads $(threads) )$(if $(debug),-d )$(if $(static),--static )$(if $(LDFLAGS),--link-flags="$(LDFLAGS)" )
 SPEC_FLAGS := $(if $(verbose),-v )$(if $(junit_output),--junit_output $(junit_output) )
 CRYSTAL_CONFIG_BUILD_COMMIT := $(shell git rev-parse --short HEAD 2> /dev/null)
 EXPORTS := $(if $(release),,CRYSTAL_CONFIG_PATH="$(PWD)/src") CRYSTAL_CONFIG_BUILD_COMMIT="$(CRYSTAL_CONFIG_BUILD_COMMIT)"