py/mkenv.mk: Move usage of 32-bit flags to py.mk.

This allows ports/variants to configure MICROPY_FORCE_32BIT after including
mkenv.mk, but before py.mk.

py/mkenv.mk

@@ -55,11 +55,6 @@ OBJCOPY = $(CROSS_COMPILE)objcopy
 SIZE = $(CROSS_COMPILE)size
 STRIP = $(CROSS_COMPILE)strip
 AR = $(CROSS_COMPILE)ar
-ifeq ($(MICROPY_FORCE_32BIT),1)
-CC += -m32
-CXX += -m32
-LD += -m32
-endif
 
 MAKE_MANIFEST = $(PYTHON) $(TOP)/tools/makemanifest.py
 MAKE_FROZEN = $(PYTHON) $(TOP)/tools/make-frozen.py

py/py.mk

@@ -21,6 +21,13 @@ QSTR_GLOBAL_REQUIREMENTS += $(HEADER_BUILD)/mpversion.h
 # some code is performance bottleneck and compiled with other optimization options
 CSUPEROPT = -O3
 
+# Enable building 32-bit code on 64-bit host.
+ifeq ($(MICROPY_FORCE_32BIT),1)
+CC += -m32
+CXX += -m32
+LD += -m32
+endif
+
 # External modules written in C.
 ifneq ($(USER_C_MODULES),)
 # pre-define USERMOD variables as expanded so that variables are immediate