Terin Stock <terinjokes@gmail.com> writes:

...

Could it be that Clang is lying to autoconf in Xcode 4.3, pretending to be GCC? Maybe it would be worth investigating, and filing a bug against Clang or Autoconf, if appropriate.

It's possible this is the case, my configure output:

checking whether we are using the GNU C compiler… yes

It looks like autoconf checks for the GCC C compiler by seeing if __GNUC__ is defined. If it is, the code is compiled and no errors happen. If it isn't, it fails to compile, and autoconf treats that as not being the C compiler.

Maybe this is a Clang bug then. If Clang wants to pretend it is GCC, then it needs to work the same way... Perhaps a bug should be filed against Clang that the preprocessor option -dI is not working correctly (especially since Clang apparently accepts the option without error, so they seem to have intended to implement it). If you can come up with something for configure.in that works-around the Clang problem until it might be fixed we will be happy to include it (it should be possible to do without changing autoconf itself). - Kristian.