* Don't overwrite CFLAGS
* Respect CPPFLAGS

--- a/Makefile
+++ b/Makefile
@@ -66,7 +66,7 @@
 ifdef CONFIG_CLANG
   HOST_CC=clang
   CC=$(CROSS_PREFIX)clang
-  CFLAGS=-g -Wall -MMD -MF $(OBJDIR)/$(@F).d
+  CFLAGS += -Wall -MMD -MF $(OBJDIR)/$(@F).d
   CFLAGS += -Wextra
   CFLAGS += -Wno-sign-compare
   CFLAGS += -Wno-missing-field-initializers
@@ -87,7 +87,7 @@
 else
   HOST_CC=gcc
   CC=$(CROSS_PREFIX)gcc
-  CFLAGS=-g -Wall -MMD -MF $(OBJDIR)/$(@F).d
+  CFLAGS += -Wall -MMD -MF $(OBJDIR)/$(@F).d
   CFLAGS += -Wno-array-bounds -Wno-format-truncation
   ifdef CONFIG_LTO
     AR=$(CROSS_PREFIX)gcc-ar
@@ -110,7 +110,7 @@
 CFLAGS+=$(DEFINES)
 CFLAGS_DEBUG=$(CFLAGS) -O0
 CFLAGS_SMALL=$(CFLAGS) -Os
-CFLAGS_OPT=$(CFLAGS) -O2
+CFLAGS_OPT=$(CFLAGS)
 CFLAGS_NOLTO:=$(CFLAGS_OPT)
 LDFLAGS=-g
 ifdef CONFIG_LTO
@@ -269,7 +269,7 @@
 	$(CC) $(CFLAGS_OPT) -fPIC -DJS_SHARED_LIBRARY -c -o $@ $<
 
 $(OBJDIR)/%.nolto.o: %.c | $(OBJDIR)
-	$(CC) $(CFLAGS_NOLTO) -c -o $@ $<
+	$(CC) $(CFLAGS_NOLTO) $(CPPFLAGS) -c -o $@ $<
 
 $(OBJDIR)/%.m32.o: %.c | $(OBJDIR)
 	$(CC) -m32 $(CFLAGS_OPT) -c -o $@ $<