[Bug libstdc++/103650] New: [9/10/11/12 Regression] libstdc++ headers defined LT_OBJDIR and STDC_HEADERS

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103650

            Bug ID: 103650
           Summary: [9/10/11/12 Regression] libstdc++ headers defined
                    LT_OBJDIR and STDC_HEADERS
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#define LT_OBJDIR 99
#define STDC_HEADERS 99
#include <utility>
#if LT_OBJDIR != 99
# error LT_OBJDIR redefined
#endif
#if STDC_HEADERS != 99
# error STDC_HEADERS redefined
#endif


In file included from /usr/include/c++/11/utility:68,
                 from macros.C:3:
macros.C:4:5: error: token "".libs/"" is not valid in preprocessor expressions
    4 | #if LT_OBJDIR != 99
      |     ^~~~~~~~~
macros.C:8:3: error: #error STDC_HEADERS redefined
    8 | # error STDC_HEADERS redefined
      |   ^~~~~


With GCC 4.1 only STDC_HEADERS was defined:

macros.C:8:3: error: #error STDC_HEADERS redefined

So the definition of LT_OBJDIR in 4.3 and later (I can't check 4.2) is a
regression.

We never asked for those macros, this is libtool and autoconf being "helpful".