Darwin/aarch64: Fix invalid reference in assembly
Darwin/aarch64: Restrict .size to ELF like arm32.
Darwin/aarch64: Account for long double being equal to double

According to the iOS ABI Reference, long double is identical to
double in iOS, and will configure as such.
Darwin/aarch64: Inhibit Xcode warning
Darwin/aarch64: Use Clang cache invalidation builtin
Darwin/aarch64: Fix "shadows declaration" warnings
Darwin/aarch64: size_t assumptions