when passing the offset parameter to mmap it is ignored by the msync operation occuring on munmap

I hit this when compiling libgit2 with emscripten:
https://github.com/petersalomonsen/libgit2/blob/emscripten-support/src/indexer.c#L618

applying #10095 fixes the issue for me and makes it possible to clone using libgit2 compiled with emscripten (libgit2/libgit2#5345)