Unify sorted asserts to use the existing atomic pattern

These are all benign races and only visible in !NDEBUG. tsan complains
about it, but a simple atomic bool is sufficient to make it happy.

llvm-svn: 335823
diff --git a/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
index 439ba9e..2f3390d 100644
--- a/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
+++ b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
@@ -415,11 +415,11 @@
 static const NEONLdStTableEntry *LookupNEONLdSt(unsigned Opcode) {
 #ifndef NDEBUG
   // Make sure the table is sorted.
-  static bool TableChecked = false;
-  if (!TableChecked) {
+  static std::atomic<bool> TableChecked(false);
+  if (!TableChecked.load(std::memory_order_relaxed)) {
     assert(std::is_sorted(std::begin(NEONLdStTable), std::end(NEONLdStTable)) &&
            "NEONLdStTable is not sorted!");
-    TableChecked = true;
+    TablesChecked.store(true, std::memory_order_relaxed);
   }
 #endif