Suppress -Wincompatible-pointer-types when needed

[knu]

LLVM Clang 22+ treats -Wincompatible-pointer-types as an error by default, 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 when the compiler rejects an unsigned long to uint64_t pointer conversion, as a workaround until the type mismatch is properly fixed in the extension source.

Ref: #359
Ref: #361

[tisba]

Hey! I added macOS 26 (both on arm and x86) to the CI matrix: #398. It seems to compile just fine, even without your change… 🤔 The images use clang 17, according to https://github.com/actions/runner-images/blob/main/images/macos/macos-15-arm64-Readme.md.

Maybe there is another cause for the compilation issues?

EDIT: The referenced issues mention this problem also happening on older macOS versions, not only macOS 26.

[knu]

@tisba Sorry, the build process picked Clang 22 installed via Homebrew, which was the cause. I've updated the fix.

https://github.com/llvm/llvm-project/blob/llvmorg-22.1.0/clang/docs/ReleaseNotes.rst#c-c-language-potentially-breaking-changes

[tisba]

Thank you. This greatly exceeds my level of expertise though 😅

Maybe @SamSaffron @bnoordhuis can take a look?

[knu]

The added conditional basically checks if the compiler accepts -Wincompatible-pointer-types and if such a warning counts as a hard error, and we add -Wno-incompatible-pointer-types to CFLAGS if that's the case.

[bnoordhuis]

Wouldn't this also solve the issue?

diff --git a/ext/mini_racer_extension/serde.c b/ext/mini_racer_extension/serde.c
index 7d5d51f..3a3d8eb 100644
--- a/ext/mini_racer_extension/serde.c
+++ b/ext/mini_racer_extension/serde.c
@@ -244,7 +244,7 @@ static void ser_num(Ser *s, double v)
 }
 
 // ser_bigint: |n| is in bytes, not quadwords
-static void ser_bigint(Ser *s, const uint64_t *p, size_t n, int sign)
+static void ser_bigint(Ser *s, const unsigned long *p, size_t n, int sign)
 {
     if (*s->err)
         return;