mpy-cross: Disable stack check when building with Emscripten.

`mpy-cross` can be compiled to WASM using Emscripten, but it is not happy
unless the stack check is disabled.

Signed-off-by: David Lechner <david@pybricks.com>

mpy-cross/mpconfigport.h

@@ -62,7 +62,9 @@
 #define MICROPY_READER_POSIX        (1)
 #define MICROPY_ENABLE_RUNTIME      (0)
 #define MICROPY_ENABLE_GC           (1)
+#ifndef __EMSCRIPTEN__
 #define MICROPY_STACK_CHECK         (1)
+#endif
 #define MICROPY_HELPER_LEXER_UNIX   (1)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_ENABLE_SOURCE_LINE  (1)