Need to instantiate the linker and assembler slightly differently now 
that we're no longer using the internal GetTools call.

…e argument

Unfortunately, while the user is no longer required to specify a command
line argument to the user, the compiler still needs a new Option for
information to be pushed from the Driver onto both the host and device
for now. If it's just device related, it would be feasible to check the
Target triple. Sadly the host invocation doesn't contain any knowledge
of the offloaded triple from what I can tell (aux-triple would be nice
to use, but it seems this is largelly used to pass host triple
information to device offloading passes and not vice-versa).

Changed -fsycl-xocc-device -> -fsycl-xocc, as it currently enforces both
host and device related tweaks (mainly forces the host definition of
__SYCL_XILINX_ONLY__, which I think should be refactored out long term
for a runtime solution if feasible).

Moved option -fsycl-xocc from Options.td to CC1Options.td, as it's more
"Clang" specific rather than part of the driver frontend at the moment
(shouldn't really be read by the driver/isn't at the moment). Perhaps, a
bit pedantic...

Adding a test to check internal compiler defines that should print some
messages based on some defines that should be generated by the compiler.

Should be an NFC, but simplifies and cleans up the implementation a 
little.

This shouldn't change any existing functionallity, it is cleaning the 
driver by:
 * Moving construct commands from the XOCC Tool Chain into the sycl-xocc 
shell script, resulting in 1 single command for the Tool Chain to the 
script
 * Combining the XOCC Compiler and Linker Command phases into one, in 
both the Script and commands

Overall this should result in a much easier to read and understand set 
of tools to build on.

* Fixed documentation and tests to use new fsycl-targets
* Added RUN: true to the top of new test so that it passes by default 
with check-all
* Removed some old todo's from XOCC.h

…oadKind

I think this makes more snese than the previous version that used the 
Arch > OS categorization method like GetToolChain.

Open to changing it back though or altering it to a different 
categorization method!

Largelly just tidying up the new test and documentation, nothing 
important.