Support dynamic location for flash bank offset

Fix static asserts so they don't fail to compile if the flash bank
location is inside the binary itself.

Fixes #1278

src/rp2_common/pico_btstack/btstack_flash_bank.c

@@ -12,7 +12,7 @@
 // Check sizes
 static_assert(PICO_FLASH_BANK_TOTAL_SIZE % (FLASH_SECTOR_SIZE * 2) == 0, "PICO_FLASH_BANK_TOTAL_SIZE invalid");
 static_assert(PICO_FLASH_BANK_TOTAL_SIZE <= PICO_FLASH_SIZE_BYTES, "PICO_FLASH_BANK_TOTAL_SIZE too big");
-static_assert(PICO_FLASH_BANK_STORAGE_OFFSET + PICO_FLASH_BANK_TOTAL_SIZE <= PICO_FLASH_SIZE_BYTES, "PICO_FLASH_BANK_TOTAL_SIZE too big");
+static_assert(__builtin_constant_p(PICO_FLASH_BANK_STORAGE_OFFSET) ? PICO_FLASH_BANK_STORAGE_OFFSET + PICO_FLASH_BANK_TOTAL_SIZE <= PICO_FLASH_SIZE_BYTES : 1, "PICO_FLASH_BANK_TOTAL_SIZE too big");
 
 // Size of one bank
 #define PICO_FLASH_BANK_SIZE (PICO_FLASH_BANK_TOTAL_SIZE / 2)
@@ -133,11 +133,10 @@ static const hal_flash_bank_t pico_flash_bank_instance_obj = {
 };
 
 const hal_flash_bank_t *pico_flash_bank_instance(void) {
-
 #ifndef NDEBUG
     // Check we're not overlapping the binary in flash
     extern char __flash_binary_end;
-    assert((uintptr_t)&__flash_binary_end - XIP_BASE <= PICO_FLASH_BANK_STORAGE_OFFSET);
+    assert(__builtin_constant_p(PICO_FLASH_BANK_STORAGE_OFFSET) ? ((uintptr_t)&__flash_binary_end - XIP_BASE <= PICO_FLASH_BANK_STORAGE_OFFSET) : true);
 #endif
 
     return &pico_flash_bank_instance_obj;