Define portNOP in RP2040 port (#1003)

portable/ThirdParty/GCC/RP2040/include/portmacro.h

diff --git a/portable/ThirdParty/GCC/RP2040/include/portmacro.h b/portable/ThirdParty/GCC/RP2040/include/portmacro.h
index 1fe5e41..bf91eda 100644
--- a/portable/ThirdParty/GCC/RP2040/include/portmacro.h
+++ b/portable/ThirdParty/GCC/RP2040/include/portmacro.h
@@ -278,7 +278,7 @@
 #define portTASK_FUNCTION_PROTO( vFunction, pvParameters )    void vFunction( void * pvParameters )
 #define portTASK_FUNCTION( vFunction, pvParameters )          void vFunction( void * pvParameters )
 
-#define portNOP()
+#define portNOP()               __asm volatile ( "nop" )
 
 #define portMEMORY_BARRIER()    __asm volatile ( "" ::: "memory" )