extmod/modwebrepl: Add config option to put filebuf[512] on stack/bss.

Since the esp8266 has a small stack this buffer is kept in the BSS.

extmod/modwebrepl.c

@@ -245,7 +245,11 @@ STATIC mp_uint_t _webrepl_read(mp_obj_t self_in, void *buf, mp_uint_t size, int
     }
 
     if (self->data_to_recv != 0) {
-        static byte filebuf[512];
+        // Ports that don't have much available stack can make this filebuf static
+        #if MICROPY_PY_WEBREPL_STATIC_FILEBUF
+        static
+        #endif
+        byte filebuf[512];
         filebuf[0] = *(byte*)buf;
         mp_uint_t buf_sz = 1;
         if (--self->data_to_recv != 0) {

ports/esp8266/mpconfigport.h

@@ -90,6 +90,7 @@
 #define MICROPY_PY_UWEBSOCKET       (1)
 #define MICROPY_PY_WEBREPL          (1)
 #define MICROPY_PY_WEBREPL_DELAY    (20)
+#define MICROPY_PY_WEBREPL_STATIC_FILEBUF (1)
 #define MICROPY_PY_FRAMEBUF         (1)
 #define MICROPY_PY_MICROPYTHON_MEM_INFO (1)
 #define MICROPY_PY_OS_DUPTERM       (2)