ports/windows: Add comment about compiler disable limitation.

Document that MICROPY_ENABLE_COMPILER cannot be disabled in the pydfu
variant because the build system unconditionally enables
MICROPY_MODULE_FROZEN_STR which requires the compiler.

Also add ifndef guard for MICROPY_HELPER_REPL to allow variant override.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/windows/variants/pydfu/mpconfigvariant.h

@@ -27,6 +27,10 @@
 // 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.
+
 // Disable modules not needed by pydfu
 #define MICROPY_PY_JSON                     (0)
 #define MICROPY_PY_RE                       (0)