Fix Clang 21+ -Wuninitialized-const-pointer warning when using MSan

Co-authored-by: Tim Ruffing <[email protected]>

Author: hebasto

src/checkmem.h

@@ -48,7 +48,16 @@
 #  if __has_feature(memory_sanitizer)
 #    include <sanitizer/msan_interface.h>
 #    define SECP256K1_CHECKMEM_ENABLED 1
-#    define SECP256K1_CHECKMEM_UNDEFINE(p, len) __msan_allocated_memory((p), (len))
+#    if defined(__clang__)
+#      define SECP256K1_CHECKMEM_UNDEFINE(p, len) do { \
+         _Pragma("clang diagnostic push") \
+         _Pragma("clang diagnostic ignored \"-Wuninitialized-const-pointer\"") \
+         __msan_allocated_memory((p), (len)); \
+         _Pragma("clang diagnostic pop") \
+         } while(0)
+#    else
+#      define SECP256K1_CHECKMEM_UNDEFINE(p, len) __msan_allocated_memory((p), (len))
+#    endif
 #    define SECP256K1_CHECKMEM_DEFINE(p, len) __msan_unpoison((p), (len))
 #    define SECP256K1_CHECKMEM_MSAN_DEFINE(p, len) __msan_unpoison((p), (len))
 #    define SECP256K1_CHECKMEM_CHECK(p, len) __msan_check_mem_is_initialized((p), (len))