[ms-inline asm] Rework the front-end to use the API introduced in r165946.

-The front-end now builds a single assembly string and feeds it to the
 AsmParser.  The front-end iterates on a per statement basis by calling the
 ParseStatement() function.  Please note, the calling of ParseStatement() and
 and any notion of MCAsmParsedOperands will be sunk into the MC layer in the
 near future.  I plan to expose more basic APIs such as getClobbers, etc.

-The enumeration of the AsmString expressions have been reworked to use SMLocs
 rather than assembly Pieces, which were being parsed in the front-end.

-The test case, t8(), was modified due to r129223.  I'll have to find a way to
 work around things such as these.

Sorry for the large commit, but breaking this in multiple smaller commits proved
too irritating.

llvm-svn: 165957