[OpenMP] Fix mispelled attribute and warning

Summary:
This is spelled `ompx_aligned_barrier` when used directly, but wasn't
included in the list of known assumptions. Fix that so now th test
works.

llvm/lib/IR/Assumptions.cpp

@@ -108,4 +108,5 @@ StringSet<> llvm::KnownAssumptionStrings({
     "omp_no_parallelism",     // OpenMP 5.1
     "ompx_spmd_amenable",     // OpenMPOpt extension
     "ompx_no_call_asm",       // OpenMPOpt extension
+    "ompx_aligned_barrier",   // OpenMPOpt extension
 });

offload/DeviceRTL/CMakeLists.txt

@@ -100,7 +100,6 @@ set(bc_flags -c -foffload-lto -std=c++17 -fvisibility=hidden
              -nocudalib -nogpulib -nogpuinc -nostdlibinc
              -fopenmp -fopenmp-cuda-mode
              -Wno-unknown-cuda-version -Wno-openmp-target
-             -Wno-unknown-assumption  # TODO: Fix false-positive warning for ext_aligned_barrier
              -DOMPTARGET_DEVICE_RUNTIME
              -I${include_directory}
              -I${devicertl_base_directory}/../include

offload/DeviceRTL/include/Synchronization.h

@@ -197,7 +197,7 @@ void threads(atomic::OrderingTy Ordering);
 /// (hence all threads in the block are "aligned"). Also perform a fence before
 /// and after the barrier according to \p Ordering. Note that the
 /// fence might be part of the barrier if the target offers this.
-[[gnu::noinline, omp::assume("ext_aligned_barrier")]] void
+[[gnu::noinline, omp::assume("ompx_aligned_barrier")]] void
 threadsAligned(atomic::OrderingTy Ordering);
 
 ///}

offload/test/jit/empty_kernel.inc

@@ -33,9 +33,9 @@ int main(int argc, char** argv) {
 }
 
 // Check for an empty kernel (IR level)
-// FIRST:       define weak_odr {{.*}} void @__omp_offloading_{{.*}}_main
+// FIRST:       define weak_odr {{.*}} void @__omp_offloading_{{.*}}_main{{.*}}
 // FIRST-NEXT:    ret void
 
 // Check for two empty kernels (IR level)
-// SECOND:      define weak_odr {{.*}} void @__omp_offloading_{{.*}}_main
+// SECOND:      define weak_odr {{.*}} void @__omp_offloading_{{.*}}_main{{.*}}
 // SECOND-NEXT:   ret void