[OPENMP 4.0] Support for 'aligned' clause in 'declare simd' directive.

The aligned clause declares that the object to which each list item points is aligned to the number of bytes expressed in the optional parameter of the aligned clause.
'aligned' '(' <argument-list> [ ':' <alignment> ] ')'
The optional parameter of the aligned clause, alignment, must be a constant positive integer expression. If no optional parameter is specified, implementation-defined default alignments for SIMD instructions on the target platforms are assumed.
The special this pointer can be used as if was one of the arguments to the function in any of the linear, aligned, or uniform clauses.

llvm-svn: 266052