c++: simplify a default construction

[Akim Demaille]

commit 2deb6874465f5b3fc6ced7241809321dc85ecdae
Author: Akim Demaille <akim.demai...@gmail.com>
Date:   Sat Nov 10 16:59:09 2018 +0100

    c++: simplify a default construction
    
    * data/lalr1.cc (yytnamerr_): here.

diff --git a/data/lalr1.cc b/data/lalr1.cc
index 936dacd1..8706eda6 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -522,7 +522,7 @@ m4_if(b4_prefix, [yy], [],
   {
     if (*yystr == '"')
       {
-        std::string yyr = "";
+        std::string yyr;
         char const *yyp = yystr;
 
         for (;;)