diff --git a/Makefile b/Makefile
index e6ae827..bbd3ce8 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,8 @@ CONFIG_LTO=y
 #CONFIG_WERROR=y
 # force 32 bit build for some utilities
 #CONFIG_M32=y
+# build with -Os instead of -O2
+#CONFIG_SMALL=y
 
 ifdef CONFIG_DARWIN
 # use clang instead of gcc
@@ -52,6 +54,13 @@ CONFIG_BIGNUM=y
 
 OBJDIR=.obj
 
+CFLAGS_ENV:=$(CFLAGS)
+LDFLAGS_ENV:=$(LDFLAGS)
+
+HOST_BUILD=
+CFLAGS=$(if $(HOST_BUILD),,$(CFLAGS_ENV))
+LDFLAGS=$(if $(HOST_BUILD),,$(LDFLAGS_ENV))
+
 ifdef CONFIG_WIN32
   ifdef CONFIG_M32
     CROSS_PREFIX=i686-w64-mingw32-
@@ -66,7 +75,7 @@ endif
 ifdef CONFIG_CLANG
   HOST_CC=clang
   CC=$(CROSS_PREFIX)clang
-  CFLAGS=-g -Wall -MMD -MF $(OBJDIR)/$(@F).d
+  CFLAGS += -g -Wall -MMD -MF $(OBJDIR)/$(@F).d
   CFLAGS += -Wextra
   CFLAGS += -Wno-sign-compare
   CFLAGS += -Wno-missing-field-initializers
@@ -87,7 +96,7 @@ ifdef CONFIG_CLANG
 else
   HOST_CC=gcc
   CC=$(CROSS_PREFIX)gcc
-  CFLAGS=-g -Wall -MMD -MF $(OBJDIR)/$(@F).d
+  CFLAGS += -g -Wall -MMD -MF $(OBJDIR)/$(@F).d
   CFLAGS += -Wno-array-bounds -Wno-format-truncation
   ifdef CONFIG_LTO
     AR=$(CROSS_PREFIX)gcc-ar
@@ -110,9 +119,13 @@ endif
 CFLAGS+=$(DEFINES)
 CFLAGS_DEBUG=$(CFLAGS) -O0
 CFLAGS_SMALL=$(CFLAGS) -Os
+ifdef CONFIG_SMALL
+CFLAGS_OPT=$(CFLAGS) -Os
+else
 CFLAGS_OPT=$(CFLAGS) -O2
+endif
 CFLAGS_NOLTO:=$(CFLAGS_OPT)
-LDFLAGS=-g
+LDFLAGS+=-g
 ifdef CONFIG_LTO
 CFLAGS_SMALL+=-flto
 CFLAGS_OPT+=-flto
@@ -175,7 +188,7 @@ QJS_OBJS+=$(OBJDIR)/qjscalc.o
 endif
 
 HOST_LIBS=-lm -ldl -lpthread
-LIBS=-lm
+LIBS+=-lm
 ifndef CONFIG_WIN32
 LIBS+=-ldl -lpthread
 endif
@@ -194,6 +207,8 @@ qjsc$(EXE): $(OBJDIR)/qjsc.o $(QJS_LIB_OBJS)
 
 ifneq ($(CROSS_PREFIX),)
 
+$(QJSC): HOST_BUILD=1
+
 $(QJSC): $(OBJDIR)/qjsc.host.o \
     $(patsubst %.o, %.host.o, $(QJS_LIB_OBJS))
 	$(HOST_CC) $(LDFLAGS) -o $@ $^ $(HOST_LIBS)
@@ -261,6 +276,8 @@ run-test262-32: $(patsubst %.o, %.m32.o, $(OBJDIR)/run-test262.o $(QJS_LIB_OBJS)
 $(OBJDIR)/%.o: %.c | $(OBJDIR)
 	$(CC) $(CFLAGS_OPT) -c -o $@ $<
 
+$(OBJDIR)/%.host.o: HOST_BUILD=1
+
 $(OBJDIR)/%.host.o: %.c | $(OBJDIR)
 	$(HOST_CC) $(CFLAGS_OPT) -c -o $@ $<
 
@@ -285,6 +302,8 @@ $(OBJDIR)/%.check.o: %.c | $(OBJDIR)
 regexp_test: libregexp.c libunicode.c cutils.c
 	$(CC) $(LDFLAGS) $(CFLAGS) -DTEST -o $@ libregexp.c libunicode.c cutils.c $(LIBS)
 
+unicode_gen: HOST_BUILD=1
+
 unicode_gen: $(OBJDIR)/unicode_gen.host.o $(OBJDIR)/cutils.host.o libunicode.c unicode_gen_def.h
 	$(HOST_CC) $(LDFLAGS) $(CFLAGS) -o $@ $(OBJDIR)/unicode_gen.host.o $(OBJDIR)/cutils.host.o