py/mkrules.mk: Make MICROPY_MODULE_FROZEN_STR conditional on compiler.

When MICROPY_ENABLE_COMPILER=0, MICROPY_MODULE_FROZEN_STR defaults to 0
since frozen .py source files require the compiler at runtime. Only
pre-compiled .mpy bytecode can be used without the compiler.

Also pass MICROPY_ENABLE_COMPILER=0 to CFLAGS when explicitly set.

ports/windows/variants/pydfu: Disable compiler for frozen .mpy only.

The pydfu variant uses only pre-compiled frozen .mpy modules, so the
compiler is not needed. This reduces binary size by ~90KB.

Tested on Unix port with MICROPY_ENABLE_COMPILER=0 - frozen modules
execute correctly without the compiler.

Author: pi-anl

ports/windows/variants/pydfu/mpconfigvariant.h

@@ -26,10 +26,8 @@
 
 // Minimal variant for pydfu standalone application.
 // Disables features not needed to reduce binary size.
-
-// Note: MICROPY_ENABLE_COMPILER cannot be disabled because the build system
-// unconditionally enables MICROPY_MODULE_FROZEN_STR which requires the compiler.
-// This is a MicroPython core limitation.
+// The compiler is disabled via mpconfigvariant.mk since only frozen .mpy
+// bytecode is used.
 
 // Disable modules not needed by pydfu
 #define MICROPY_PY_JSON                     (0)

ports/windows/variants/pydfu/mpconfigvariant.mk

@@ -1,4 +1,6 @@
 # Minimal variant for pydfu standalone application.
 # Enables FFI for pyusb to call libusb.
+# Disables compiler since only frozen .mpy bytecode is used.
 
 MICROPY_PY_FFI = 1
+MICROPY_ENABLE_COMPILER = 0

py/mkrules.mk

@@ -212,7 +212,23 @@ endif
 # Set compile options needed to enable frozen code.
 CFLAGS += -DMICROPY_QSTR_EXTRA_POOL=mp_qstr_frozen_const_pool
 CFLAGS += -DMICROPY_MODULE_FROZEN_MPY
+
+# MICROPY_MODULE_FROZEN_STR enables freezing .py files as source text that
+# requires the compiler at runtime. If the compiler is disabled, default this
+# to 0 since only pre-compiled .mpy files can be used.
+ifeq ($(MICROPY_ENABLE_COMPILER),0)
+MICROPY_MODULE_FROZEN_STR ?= 0
+else
+MICROPY_MODULE_FROZEN_STR ?= 1
+endif
+ifneq ($(MICROPY_MODULE_FROZEN_STR),0)
 CFLAGS += -DMICROPY_MODULE_FROZEN_STR
+endif
+
+# Pass MICROPY_ENABLE_COMPILER to CFLAGS if explicitly set.
+ifeq ($(MICROPY_ENABLE_COMPILER),0)
+CFLAGS += -DMICROPY_ENABLE_COMPILER=0
+endif
 
 # Set default path variables to be passed to makemanifest.py. These will be
 # available in path substitutions. Additional variables can be set per-board