[AutoFDO] Add hierarchical discriminator for loop versioning

[AutoFDO] Add hierarchical discriminator for loop versioning

Add hierarchical discriminator support for loop versioning pass.
Assigns copyid discriminators to distinguish different loop versions.

gcc/ChangeLog:

	* gimple-loop-versioning.cc (loop_versioning::version_loop): Assign
	copyid discriminators to distinguish different loop versions.

gcc/testsuite/ChangeLog:

	* gcc.dg/hierarchical-discriminator-loop-version.c: New test.

Signed-off-by: Kugan Vivekanandarajah <kvivekananda@nvidia.com>