[openacc] Disable pass_thread_jumps for IFN_UNIQUE

[openacc] Disable pass_thread_jumps for IFN_UNIQUE

If we compile the openacc testcase with -fopenacc -O2, we run into a SIGSEGV
or assert.  The root cause for this is that pass_thread_jumps breaks the
invariant that OACC_FORK and OACC_JOIN mark the start and end of a
single-entry-single-exit region.

Fix this by bailing out when encountering an IFN_UNIQUE in
thread_jumps::profitable_jump_thread_path.

Bootstrapped and reg-tested on x86_64.
Build and reg-tested libgomp on x86_64 with nvptx accelerator.

2019-06-15  Tom de Vries  <tdevries@suse.de>

	PR tree-optimization/90009
	* tree-ssa-threadbackward.c (thread_jumps::profitable_jump_thread_path):
	Return NULL if bb contains IFN_UNIQUE.

	* testsuite/libgomp.oacc-c-c++-common/pr90009.c: New test.

From-SVN: r272321