Small PICO_PLATFORM=host fixes (#639)

src/host/hardware_gpio/include/hardware/gpio.h

@@ -152,7 +152,9 @@ void gpio_set_dir_all_bits(uint32_t value);
 void gpio_set_dir(uint gpio, bool out);
 
 // debugging
+#ifndef PICO_DEBUG_PIN_BASE
 #define PICO_DEBUG_PIN_BASE 19u
+#endif
 
 // note these two macros may only be used once per compilation unit
 #define CU_REGISTER_DEBUG_PINS(p, ...)

src/host/pico_platform/include/pico/platform.h

@@ -27,8 +27,8 @@ extern "C" {
 #define __scratch_x(group)
 #define __scratch_y(group)
 
-#define __packed_aligned
-#define __packed
+#define __packed __attribute__((packed))
+#define __packed_aligned __packed __attribute((aligned))
 
 #define __time_critical_func(x) x
 #define __after_data(group)