Fix watchOS and visionOS for pread64 and pwrite64 calls

[simlay]

In #122880, links to preadv64 and pwritev64 were added for watchOS however the underlying weak! macro did not include target_os = "watchos".

This resulted in an xcodebuild error when targeting watchOS:

Undefined symbols for architecture arm64:
  "_preadv64", referenced from:
      __rust_extern_with_linkage_preadv64 in libliveview_native_core.a[274](std-324fdd8d31e8eaa2.std.e18cf7e8d0336778-cgu.08.rcgu.o)
  "_pwritev64", referenced from:
      __rust_extern_with_linkage_pwritev64 in libliveview_native_core.a[274](std-324fdd8d31e8eaa2.std.e18cf7e8d0336778-cgu.08.rcgu.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

So I added them. I also went ahead and added the same for visionOS because it's bound to create the same issue.