[runtime] Mark swift_stdlib_malloc_size as being readnone.
[runtime] Mark swift_stdlib_malloc_size as being readnone.

This entry point /does/ read memory but this is not memory that is
visible to the compiler.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift