[Bug bootstrap/100731] New: GCC 11 fails to build using GCC 4.8 because of missing includes

["harald at gigawatt dot nl" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100731

            Bug ID: 100731
           Summary: GCC 11 fails to build using GCC 4.8 because of missing
                    includes
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: harald at gigawatt dot nl
  Target Milestone: ---

When building GCC 11 with GCC 4.8 on a platform without _GLIBCXX_USE_C99, the
build fails. The result is:

../../gcc-11.1.0/c++tools/server.cc: In function ‘void internal_error(const
char*, ...)’:
../../gcc-11.1.0/c++tools/server.cc:199:10: error: ‘exit’ was not declared in
this scope
   exit (2);
          ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void error(const char*,
...)’:
../../gcc-11.1.0/c++tools/server.cc:233:10: error: ‘exit’ was not declared in
this scope
   exit (1);
          ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void print_usage(int)’:
../../gcc-11.1.0/c++tools/server.cc:284:15: error: ‘exit’ was not declared in
this scope
   exit (status);
               ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void print_version()’:
../../gcc-11.1.0/c++tools/server.cc:299:10: error: ‘exit’ was not declared in
this scope
   exit (0);
          ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘int
maybe_parse_socket(std::string&, module_resolver*)’:
../../gcc-11.1.0/c++tools/server.cc:828:48: error: ‘strtoul’ was not declared
in this scope
    unsigned port = strtoul (cptr + 1, &endp, 10);
                                                ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void internal_error(const
char*, ...)’:
../../gcc-11.1.0/c++tools/server.cc:200:1: warning: ‘noreturn’ function does
return [enabled by default]
 }
 ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void print_version()’:
../../gcc-11.1.0/c++tools/server.cc:300:1: warning: ‘noreturn’ function does
return [enabled by default]
 }
 ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void print_usage(int)’:
../../gcc-11.1.0/c++tools/server.cc:285:1: warning: ‘noreturn’ function does
return [enabled by default]
 }
 ^
../../gcc-11.1.0/c++tools/server.cc: In function ‘void error(const char*,
...)’:
../../gcc-11.1.0/c++tools/server.cc:234:1: warning: ‘noreturn’ function does
return [enabled by default]
 }
 ^

If the functions from <stdlib.h> are wanted, this file should just include
<stdlib.h> directly rather than relying on C++ headers pulling it in.

This happens for me on uclibc but is reproducible on glibc by locally modifying
GCC 4.8's c++config.h to not define _GLIBCXX_USE_C99.