Fix "make test-cp-name-parser"

src/gdb/cp-name-parser.y: In function ‘int main(int, char**)’:
src/gdb/cp-name-parser.y:2132:30: error: ISO C++ forbids converting a string constant to ‘char*’ [-Werror=write-strings]
   char *str2, *extra_chars = "", c;
                              ^

Simply don't initialize the variable, it's not necessary.

gdb/ChangeLog:
2017-11-08  Pedro Alves  <palves@redhat.com>

	* cp-name-parser.y (main): Don't initialize extra_chars.

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2017-11-08  Pedro Alves  <palves@redhat.com>
+
+	* cp-name-parser.y (main): Don't initialize extra_chars.
+
 2017-11-07  Tom Tromey  <tom@tromey.com>
 
 	* event-top.h (command_handler): Constify.

gdb/cp-name-parser.y

@@ -2129,7 +2129,7 @@ internal_error (const char *file, int line, const char *fmt, ...)
 int
 main (int argc, char **argv)
 {
-  char *str2, *extra_chars = "", c;
+  char *str2, *extra_chars, c;
   char buf[65536];
   int arg;
   const char *errmsg;