Fix attribute insertion location in the presence of "static" and a modifier

We were incorrectly ignoring the "static" because it's not in the
DeclAttributes list.

Author: DougGregor

lib/AST/Decl.cpp

@@ -4335,7 +4335,14 @@ SourceLoc Decl::getAttributeInsertionLoc(bool forModifier) const {
     return SourceLoc();
 
   SourceLoc resultLoc = getAttrs().getStartLoc(forModifier);
-  return resultLoc.isValid() ? resultLoc : introDecl->getStartLoc();
+  if (resultLoc.isInvalid())
+    return introDecl->getStartLoc();
+
+  SourceLoc startLoc = introDecl->getStartLoc();
+  if (!forModifier && getASTContext().SourceMgr.isBefore(startLoc, resultLoc))
+    return startLoc;
+
+  return resultLoc;
 }
 
 /// Returns true if \p VD needs to be treated as publicly-accessible

test/Unsafe/safe.swift

@@ -30,7 +30,7 @@ func rethrowing(body: (UnsafeType) throws -> Void) rethrows { } // expected-warn
 
 class HasStatics {
   // expected-note@+1{{make static method 'f' @unsafe to indicate that its use is not memory-safe}}{{3-3=@unsafe }}
-  static func f(_: UnsafeType) { } // expected-warning{{reference to unsafe struct 'UnsafeType' [Unsafe]}}
+  static internal func f(_: UnsafeType) { } // expected-warning{{reference to unsafe struct 'UnsafeType' [Unsafe]}}
 }
 
 @unsafe