Fix linker warnings on macOS

[xiaozhuai]

Set up MACOSX_DEPLOYMENT_TARGET correctly

ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1054](242b1992def1ef0b-helpers.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1891](44ff4c55aa9e5133-entropy_common.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1892](44ff4c55aa9e5133-error_private.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1893](44ff4c55aa9e5133-fse_decompress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1896](44ff4c55aa9e5133-zstd_common.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1897](fb80479a5fb81f6a-fse_compress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1898](fb80479a5fb81f6a-hist.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1899](fb80479a5fb81f6a-huf_compress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1900](fb80479a5fb81f6a-zstd_compress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1901](fb80479a5fb81f6a-zstd_compress_literals.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1902](fb80479a5fb81f6a-zstd_compress_sequences.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1903](fb80479a5fb81f6a-zstd_compress_superblock.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1904](fb80479a5fb81f6a-zstd_double_fast.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1905](fb80479a5fb81f6a-zstd_fast.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1906](fb80479a5fb81f6a-zstd_lazy.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1907](fb80479a5fb81f6a-zstd_ldm.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1908](fb80479a5fb81f6a-zstd_opt.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1910](88f362f13b0528ed-huf_decompress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1911](88f362f13b0528ed-zstd_ddict.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1912](88f362f13b0528ed-zstd_decompress.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1913](88f362f13b0528ed-zstd_decompress_block.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)
ld: warning: object file (target/aarch64-apple-darwin/debug/libwasmtime.a[1970](db3b6bfb95261072-gdbjit.o)) was built for newer 'macOS' version (15.5) than being linked (11.0)

[alexcrichton]

Thanks! Looks like the linking error wasn't caught on CI earlier due to this block. Could you delete that as well as part of this PR as it should no longer be necessary?

For fixing linker warnings this looks reasonable to me 👍

[xiaozhuai]

Sure, I've modified this PR.

[alexcrichton]

Oh sorry I meant deleting the code in examples/CMakeLists.txt rather than here. The additions you had here in this PR looked correct to me and my comment was about how the similar linking directive in examples/CMakeLists.txt were redundant (or at least I think they were).

In the meantime this all looks good to me so I'll flag it for merge, but if you'd like I'd be happy to merge a PR with the changes of linking to CoreFoundation