Fix standalone debug builds of the emulator.

This only affects builds performed with ./android-rebuild.sh --debug,
not normal Android/SDK builds of the emulator program.
diff --git a/Makefile.android b/Makefile.android
index 35e2fcf..a5385d4 100644
--- a/Makefile.android
+++ b/Makefile.android
@@ -16,7 +16,7 @@
     MY_OPTIM := -O0 -g
 endif
 
-MY_CFLAGS := $(CONFIG_INCLUDES) $(MY_OPTIM) -DCONFIG_MEMCHECK
+MY_CFLAGS := $(CONFIG_INCLUDES) $(MY_OPTIM)
 
 # Overwrite configuration for debug builds.
 #
@@ -25,6 +25,8 @@
                  -fno-PIC -falign-functions=0
 endif
 
+MY_CFLAGS += -DCONFIG_MEMCHECK
+
 MY_LDLIBS :=
 
 # this is needed to build the emulator on 64-bit Linux systems