[ELF] Add BYTE expression to test case for non-contiguous relro [NFC]

As well as location counter expressions. The data generating expressions
such as BYTE can generate a non-zero sized OutputSection that will report
0 until assignAddresses() is called. Add an example to the existing test
case relro-non-contiguous-script-data.s.

Differential Revision: https://reviews.llvm.org/D40732

llvm-svn: 319648