Move -DNO_VALGRIND into CPPFLAGS

Since -D sets preprocessor directives, it applies for the preprocessor not
just the C compiler proper and so belongs in CPPFLAGS rather than CFLAGS.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Makefile

@@ -43,7 +43,7 @@ HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
 
 NO_VALGRIND := $(shell $(PKG_CONFIG) --exists valgrind; echo $$?)
 ifeq ($(NO_VALGRIND),1)
-	CFLAGS += -DNO_VALGRIND
+	CPPFLAGS += -DNO_VALGRIND
 else
 	CFLAGS += $(shell $(PKG_CONFIG) --cflags valgrind)
 endif