[flang][OpenMP][test] re-add complex atomic capture regression test (#112736)

This was reverted in #110969
due to a failure on aarch64.

Weirdly aarch64 (but apparently not x86?) has a spurious phi
instruction. flang -fc1 -emit-llvm will run midle-end optimization
passes. Presumably one of those is behaving differently on different
targets. I have adapted the test to work correctly on aarch64.

The difference is in the RUN lines and the atomic exit block.

Author: tblah

flang/test/Integration/OpenMP/atomic-capture-complex.f90

@@ -0,0 +1,50 @@
+!===----------------------------------------------------------------------===!
+! This directory can be used to add Integration tests involving multiple
+! stages of the compiler (for eg. from Fortran to LLVM IR). It should not
+! contain executable tests. We should only add tests here sparingly and only
+! if there is no other way to test. Repeat this message in each test that is
+! added to this directory and sub-directories.
+!===----------------------------------------------------------------------===!
+
+!RUN: %if x86-registered-target %{ %flang_fc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fopenmp %s -o - | FileCheck --check-prefixes=CHECK,X86 %s %}
+!RUN: %if aarch64-registerd-target %{ %flang_fc1 -triple aarch64-unknown-linux-gnu -emit-llvm -fopenmp %s -o - | FileCheck --check-prefixes=CHECK,AARCH64 %s %}
+
+!CHECK: %[[X_NEW_VAL:.*]] = alloca { float, float }, align 8
+!CHECK: %[[VAL_1:.*]] = alloca { float, float }, i64 1, align 8
+!CHECK: %[[ORIG_VAL:.*]] = alloca { float, float }, i64 1, align 8
+!CHECK: store { float, float } { float 2.000000e+00, float 2.000000e+00 }, ptr %[[ORIG_VAL]], align 4
+!CHECK: br label %entry
+
+!CHECK: entry:
+!CHECK: %[[ATOMIC_TEMP_LOAD:.*]] = alloca { float, float }, align 8
+!CHECK: call void @__atomic_load(i64 8, ptr %[[ORIG_VAL]], ptr %[[ATOMIC_TEMP_LOAD]], i32 0)
+!CHECK: %[[PHI_NODE_ENTRY_1:.*]] = load { float, float }, ptr %[[ATOMIC_TEMP_LOAD]], align 8
+!CHECK: br label %.atomic.cont
+
+!CHECK: .atomic.cont
+!CHECK: %[[VAL_4:.*]] = phi { float, float } [ %[[PHI_NODE_ENTRY_1]], %entry ], [ %{{.*}}, %.atomic.cont ]
+!CHECK: %[[VAL_5:.*]] = extractvalue { float, float } %[[VAL_4]], 0
+!CHECK: %[[VAL_6:.*]] = extractvalue { float, float } %[[VAL_4]], 1
+!CHECK: %[[VAL_7:.*]] = fadd contract float %[[VAL_5]], 1.000000e+00
+!CHECK: %[[VAL_8:.*]] = fadd contract float %[[VAL_6]], 1.000000e+00
+!CHECK: %[[VAL_9:.*]] = insertvalue { float, float } undef, float %[[VAL_7]], 0
+!CHECK: %[[VAL_10:.*]] = insertvalue { float, float } %[[VAL_9]], float %[[VAL_8]], 1
+!CHECK: store { float, float } %[[VAL_10]], ptr %[[X_NEW_VAL]], align 4
+!CHECK: %[[VAL_11:.*]] = call i1 @__atomic_compare_exchange(i64 8, ptr %[[ORIG_VAL]], ptr %[[ATOMIC_TEMP_LOAD]], ptr %[[X_NEW_VAL]],
+!i32 2, i32 2)
+!CHECK: %[[VAL_12:.*]] = load { float, float }, ptr %[[ATOMIC_TEMP_LOAD]], align 4
+!CHECK: br i1 %[[VAL_11]], label %.atomic.exit, label %.atomic.cont
+
+!CHECK:   .atomic.exit
+!AARCH64: %[[LCSSA:.*]] = phi { float, float } [ %[[VAL_10]], %.atomic.cont ]
+!AARCH64: store { float, float } %[[LCSSA]], ptr %[[VAL_1]], align 4
+!X86:     store { float, float } %[[VAL_10]], ptr %[[VAL_1]], align 4
+
+program main
+      complex*8 ia, ib
+      ia = (2, 2)
+      !$omp atomic capture
+        ia = ia + (1, 1)
+        ib = ia
+      !$omp end atomic
+end program