Suppress -Wincompatible-pointer-types on macOS

Apple Clang 17+ (Xcode 26 / macOS 26) treats
-Wincompatible-pointer-types as a hard error, which breaks
compilation of mini_racer_extension.c due to the unsigned long
vs uint64_t mismatch in the bigint serialization code.

Add -Wno-incompatible-pointer-types to CFLAGS on Darwin as a
workaround until the type mismatch is properly fixed in the
extension source.

Ref: #359
Ref: #361

Author: knu

ext/mini_racer_extension/extconf.rb

@@ -32,6 +32,11 @@
 
 $CXXFLAGS += " -Wno-reserved-user-defined-literal" if IS_DARWIN
 
+# Apple Clang 17+ (Xcode 26+) treats -Wincompatible-pointer-types as an error;
+# suppress it until the `unsigned long` vs `uint64_t` mismatch in the extension
+# is properly fixed.
+$CFLAGS += " -Wno-incompatible-pointer-types" if IS_DARWIN
+
 if IS_DARWIN
   $LDFLAGS.insert(0, " -stdlib=libc++ ")
 else