[OPENMP][CUDA]Do not emit warnings for variables in late-reported asm

statements.

If the assembler instruction is not generated and the delayed diagnostic
is emitted, we may end up with extra warning message for variables used
in the asm statement. Since the asm statement is not built, the
variables may be left non-referenced and it may produce a warning about
a use of the non-initialized variables.

llvm-svn: 354928