Fix arm64 issues on mac (#3688)

Make wamrc normalize "arm64" to "aarch64v8". Previously the only way to
make the "arm64" target was to not specify a target on 64 bit arm-based
mac builds. Now arm64 and aarch64v8 are treated as the same.

Make aot_loader accept "aarch64v8" on arm-based apple (as well as
accepting legacy "arm64" based aot targets).

This also removes __APPLE__ and __MACH__ from the block that defaults
size_level to 1 since it doesn't seem to be supported for aarch64:
`LLVM ERROR: Only small, tiny and large code models are allowed on AArch64`

core/iwasm/compilation/aot_llvm.c

@@ -2790,6 +2790,15 @@ aot_create_comp_context(const AOTCompData *comp_data, aot_comp_option_t option)
                 bh_assert(vendor_sys);
                 bh_memcpy_s(default_arch, sizeof(default_arch), default_triple,
                             (uint32)(vendor_sys - default_triple));
+                /**
+                 * On Mac M[1-9]+ LLVM will report arm64 as the
+                 * architecture, for the purposes of wamr this is the
+                 * same as aarch64v8 so we'll normalize it here.
+                 */
+                if (!strcmp(default_arch, "arm64")) {
+                    bh_strcpy_s(default_arch, sizeof(default_arch),
+                                "aarch64v8");
+                }
                 arch1 = default_arch;
 
                 LLVMDisposeMessage(default_triple);