[Bug c/57201] New: Using --save-temps affects whether warning is printed

[ian at airs dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57201

             Bug #: 57201
           Summary: Using --save-temps affects whether warning is printed
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ian@airs.com


Consider this C file:

#include <stdio.h>
void
f(void)
{
  stdout;
}

When I compile it on my Ubuntu Precise system with GCC 4.8 branch with the
-Wall option, I get no error.  When I compile it with -Wall --save-temps, I get
this:

foo.c: In function ‘f’:
foo.c:5:3: warning: statement with no effect [-Wunused-value]
   stdout;
   ^

This appears to happen because <stdio.h> on my system has this line:

#define stdout stdout

When not using --save-temps, something about this is causing
linemap_location_in_system_header_p to return true for "stdout" on line 5.