RP2040: Add xPortIsInsideInterrupt to match other ARM ports (#1356)

Co-authored-by: graham sanderson <graham.sanderson@raspeberryi.com>

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 3e54f38..68686f8 100644
--- a/portable/ThirdParty/GCC/RP2040/include/portmacro.h
+++ b/portable/ThirdParty/GCC/RP2040/include/portmacro.h
@@ -149,6 +149,10 @@
         __asm volatile ( "mrs %0, IPSR" : "=r" ( ulIPSR )::); \
         ( ( uint8_t ) ulIPSR ) > 0; } )
 
+/* Use #define rather than inline method to make it easier for user code
+ * to work with kernel versions both with and without xPortIsInsideInterrupt */
+#define xPortIsInsideInterrupt() ((BaseType_t)portCHECK_IF_IN_ISR())
+
 void vYieldCore( int xCoreID );
 #define portYIELD_CORE( a )                  vYieldCore( a )