openacc: Add runtime alias checking for OpenACC kernels

openacc: Add runtime alias checking for OpenACC kernels

This commit adds the code generation for the runtime alias checks for
OpenACC loops that have been analyzed by Graphite.  The runtime alias
check condition gets generated in Graphite. It is evaluated by the
code generated for the IFN_GOACC_LOOP internal function calls.  If
aliasing is detected at runtime, the execution dimensions get adjusted
to execute the affected loops sequentially.

gcc/ChangeLog:

	* graphite-isl-ast-to-gimple.cc: Include internal-fn.h.
	(graphite_oacc_analyze_scop): Implement runtime alias checks.
	* omp-expand.cc (expand_oacc_for): Add an additional "noalias" parameter
	to GOACC_LOOP internal calls, and initialise it to integer_one_node.
	* omp-offload.cc (oacc_xform_loop): Integrate the runtime alias check
	into the GOACC_LOOP expansion.

libgomp/ChangeLog:

	* testsuite/libgomp.oacc-c-c++-common/runtime-alias-check-1.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/runtime-alias-check-2.c: New test.