re PR go/90110 (libgo fails to build against glibc 2.19)

	PR go/90110
    compiler: use temporary to avoid early destruction
    
    The code was passing a substr directly to strtol, and then checking
    the *end value returned by strtol.  But the substr could be destroyed
    as soon as strtol returns, making the test of *end invalid.
    
    Also fix an incorrect test of the string index rather than the value.
    
    Fixes https://gcc.gnu.org/PR90110
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/172663

From-SVN: r270434

gcc/go/gofrontend/MERGE

-20010e494f46d8fd58cfd372093b059578d3379a
+ecbd6562aff604b9559f63d714e922a0c9c2a77f
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/import.cc

@@ -1478,8 +1478,9 @@ Import_function_body::read_type()
   this->off_ = i + 1;
 
   char *end;
-  long val = strtol(this->body_.substr(start, i - start).c_str(), &end, 10);
-  if (*end != '\0' || i > 0x7fffffff)
+  std::string num = this->body_.substr(start, i - start);
+  long val = strtol(num.c_str(), &end, 10);
+  if (*end != '\0' || val > 0x7fffffff)
     {
       if (!this->saw_error_)
 	go_error_at(this->location(),