Add support for -all_load. Enhance DarwinLdDriverTest unit test test cases to test all options parsed so far

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@186626 91177308-0d34-0410-b5e6-96231b3b80d8
Check the return value from parse()

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@186630 91177308-0d34-0410-b5e6-96231b3b80d8