Fix build breakage from last commit (window-nat.c:windows_create_inferior)

Forgot to declare the variable 'toexec' (from
window-nat.c:windows_create_inferior) as 'const char *', which caused
a build breakage.

gdb/ChangeLog:
2017-04-12  Sergio Durigan Junior  <sergiodj@redhat.com>

	* windows-nat.c (windows_create_inferior): Declare 'toexec' as
	'const char *'.

Author: Sergio Durigan Junior

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2017-04-12  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* windows-nat.c (windows_create_inferior): Declare 'toexec' as
+	'const char *'.
+
 2017-04-12  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* common/common-utils.c (free_vector_argv): New function.

gdb/windows-nat.c

@@ -2432,7 +2432,7 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
 #else  /* !__CYGWIN__ */
   char real_path[__PMAX];
   char shell[__PMAX]; /* Path to shell */
-  char *toexec;
+  const char *toexec;
   const char *allargs = origallargs.c_str ();
   char *args, *allargs_copy;
   size_t args_len, allargs_len;