MandatoryPerformanceOptimizations: better handling of statically initialized globals which contain a pointer to another global

E.g.
```
  var p = Point(x: 10, y: 20)
  let o = UnsafePointer(&p)
```

MandatoryPerformanceOptimization must inline the accessor to the referenced global.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/ModulePasses/MandatoryPerformanceOptimizations.swift

@@ -225,7 +225,7 @@ private extension Value {
     var singleUseValue: any Value = self
     var path = SmallProjectionPath()
     while true {
-      guard let use = singleUseValue.uses.singleNonDebugUse else {
+      guard let use = singleUseValue.uses.singleRelevantUse else {
         return nil
       }
 
@@ -247,6 +247,8 @@ private extension Value {
         default:
           return nil
         }
+      case is PointerToAddressInst, is AddressToPointerInst, is BeginAccessInst:
+        break
       default:
         return nil
       }
@@ -334,3 +336,27 @@ fileprivate struct FunctionWorklist {
     }
   }
 }
+
+private extension UseList {
+  var singleRelevantUse: Operand? {
+    var singleUse: Operand?
+    for use in self {
+      switch use.instruction {
+      case is DebugValueInst,
+           // The initializer value of a global can contain access instructions if it references another
+           // global variable by address, e.g.
+           //   var p = Point(x: 10, y: 20)
+           //   let o = UnsafePointer(&p)
+           // Therefore ignore the `end_access` use of a `begin_access`.
+           is EndAccessInst:
+        continue
+      default:
+        if singleUse != nil {
+          return nil
+        }
+        singleUse = use
+      }
+    }
+    return singleUse
+  }
+}