Improve diagnostics for bad -std= flag.

Don't list deprecated -std= values (c++0x etc). Only produce one line of output
per standard, even if we know it by multiple names.

In passing, add missing -std=gnu++03 alias (supported by GCC), and add new
spelling '-std=cl1.0' for OpenCL 1.0 for consistency with the other values,
with the same meaning as the preexisting '-std=cl'.

llvm-svn: 301507