[OpenMP] Remove 'omp assumes' scopes now that we have no inline ASM (#123611)

Summary:
We used this globally scoped `ext_no_call_asm` as a sort of hack around
the compiler that allowed the attributor to optimize out inline assembly
calls to PTX instructions. Quite some time ago I got rid of every inline
assembly call and replaced it with a builitin, so this can just be
deleted.

Furthermore, I use the `[[omp::assume]]` attribute directly for the
aligned barrier usage. This prints an unknown assumption warning (even
though it isn't) so I'm just silencing that for now until I fix it
later.

---------

Co-authored-by: Michael Kruse <[email protected]>

Author: jhuber6

offload/DeviceRTL/CMakeLists.txt

@@ -100,6 +100,7 @@ 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/DeviceTypes.h

@@ -15,15 +15,6 @@
 #include <stddef.h>
 #include <stdint.h>
 
-// Tell the compiler that we do not have any "call-like" inline assembly in the
-// device rutime. That means we cannot have inline assembly which will call
-// another function but only inline assembly that performs some operation or
-// side-effect and then continues execution with something on the existing call
-// stack.
-//
-// TODO: Find a good place for this
-#pragma omp assumes ext_no_call_asm
-
 enum omp_proc_bind_t {
   omp_proc_bind_false = 0,
   omp_proc_bind_true = 1,

offload/DeviceRTL/include/Synchronization.h

@@ -192,15 +192,14 @@ void threads(atomic::OrderingTy Ordering);
 /// noinline is removed by the openmp-opt pass and helps to preserve the
 /// information till then.
 ///{
-#pragma omp begin assumes ext_aligned_barrier
 
 /// Synchronize all threads in a block, they are reaching the same instruction
 /// (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]] void threadsAligned(atomic::OrderingTy Ordering);
+[[gnu::noinline, omp::assume("ext_aligned_barrier")]] void
+threadsAligned(atomic::OrderingTy Ordering);
 
-#pragma omp end assumes
 ///}
 
 } // namespace synchronize