Description of problem:

Clang fails to compile C11 code which includes stdatomic.h. According to <https://llvm.org/bugs/show_bug.cgi?id=22740#c5>, Clang should not be looking at GCC's headers. Fedora tells Clang to look there via the --with-c-include-dirs configuration flag. Bug 893817 suggests that this flag has historically been necessary in order to successfully use libstdc++, but this no longer seems to be the case (see <https://llvm.org/bugs/show_bug.cgi?id=6907>).


Version-Release number of selected component (if applicable):

clang-3.5.0-6.fc21.x86_64

How reproducible:

Every time.

Steps to Reproduce:

Compile the following example program:

$ cat atomic.c
#include <stdatomic.h>

int f (atomic_int *p_i)
{
  return atomic_load(p_i);
}


Actual results:

$ clang -std=c11 -c atomic.c
atomic.c:5:27: error: use of undeclared identifier '__auto_type'
  return __extension__ ({ __auto_type __atomic_load_ptr = (p_i); __typeof__ (*__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; });
                          ^
atomic.c:5:79: error: use of undeclared identifier '__atomic_load_ptr'
  return __extension__ ({ __auto_type __atomic_load_ptr = (p_i); __typeof__ (*__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; });
                                                                              ^
atomic.c:5:132: error: use of undeclared identifier '__atomic_load_ptr'; did you mean '__atomic_load_tmp'?
  return __extension__ ({ __auto_type __atomic_load_ptr = (p_i); __typeof__ (*__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; });
                                                                                                                                   ^~~~~~~~~~~~~~~~~
                                                                                                                                   __atomic_load_tmp
atomic.c:5:98: note: '__atomic_load_tmp' declared here
  return __extension__ ({ __auto_type __atomic_load_ptr = (p_i); __typeof__ (*__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; });
                                                                                                 ^
atomic.c:5:10: error: returning 'void' from a function with incompatible result type 'int'
  return __extension__ ({ __auto_type __atomic_load_ptr = (p_i); __typeof__ (*__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; });
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4 errors generated.

Expected results:

Should compile with no errors. This code compiles fine with GCC, and compiles fine if clang is not passed the --with-c-include-dirs configuration flag.

Additional info:

https://llvm.org/bugs/show_bug.cgi?id=22740
https://llvm.org/bugs/show_bug.cgi?id=23556