Use -O2 optimization level by default

I noticed some weird compiler behavior when looking at strutil assembly, and sure enough the compiler optimization level was stuck at -O1. Kati is not particularly slow to compile, so I propose defaulting to -O2.

strutil_bench seems to be 16% faster with -O2.

Author: ishitatsuyuki

Makefile.ckati

@@ -70,7 +70,7 @@ KATI_CXX_TEST_EXES := $(patsubst $(KATI_INTERMEDIATES_PATH)/%.o,$(KATI_BIN_PATH)
 	$(KATI_CXX_TEST_OBJS))
 
 KATI_CXXFLAGS := -g -W -Wall -MMD -MP
-KATI_CXXFLAGS += -O -DNOLOG
+KATI_CXXFLAGS += -O2 -DNOLOG
 KATI_CXXFLAGS += -march=native
 #KATI_CXXFLAGS += -pg