[Type checker] Add ‘static’ to member operators to improve recovery.

Eliminates a crash due to missing ‘static’ on member operations. Fixes part of rdar://problem/27940842.

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -4335,6 +4335,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
                         dc->getDeclaredInterfaceType())
               .fixItInsert(FD->getAttributeInsertionLoc(/*forModifier=*/true),
                            "static ");
+
+            FD->setStatic();
           } else {
             TC.diagnose(FD->getLoc(), diag::nonfinal_operator_in_class,
                         operatorName, dc->getDeclaredInterfaceType())
@@ -4350,6 +4352,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
                     dc->getDeclaredInterfaceType())
           .fixItInsert(FD->getAttributeInsertionLoc(/*forModifier=*/true),
                        "static ");
+        FD->setStatic();
       }
     } else if (!dc->isModuleScopeContext()) {
       TC.diagnose(FD, diag::operator_in_local_scope);

test/decl/func/operator.swift

@@ -336,3 +336,12 @@ extension P3 {
   // Okay: refers to P3
   static func %%%%(lhs: P3, rhs: Unrelated) -> Unrelated { }
 }
+
+// rdar://problem/27940842 - recovery with a non-static '=='.
+class C5 {
+  func == (lhs: C5, rhs: C5) -> Bool { return false } // expected-error{{operator '==' declared in type 'C5' must be 'static'}}
+
+  func test1(x: C5) {
+    _ = x == x
+  }
+}