[SE-0458] Disambiguate "unsafe" expression within string interpolation

String interpolation uses an end-of-file token, which we weren't
checking for. Fixes rdar://146493296

Author: DougGregor

lib/Parse/ParseExpr.cpp

@@ -439,7 +439,7 @@ ParserResult<Expr> Parser::parseExprSequenceElement(Diag<> message,
   if (Tok.isContextualKeyword("unsafe") &&
       !(peekToken().isAtStartOfLine() ||
         peekToken().isAny(tok::r_paren, tok::r_brace, tok::r_square,
-                          tok::equal, tok::colon, tok::comma) ||
+                          tok::equal, tok::colon, tok::comma, tok::eof) ||
         (isExprBasic && peekToken().is(tok::l_brace)) ||
         peekToken().is(tok::period) ||
         (peekToken().isAny(tok::l_paren, tok::l_square) &&

test/Unsafe/safe.swift

@@ -207,6 +207,8 @@ func moreUnsafeFunc(unsafe: [Int]) {
   // expected-warning@-1{{no unsafe operations occur within 'unsafe' expression}}
 
   _ = unsafe[1]
+
+  _ = "\(unsafe)"
 }
 
 func yetMoreUnsafeFunc(unsafe: () -> Void) {