move debug message

[ci skip]
Several autotools fixes for clang 3.4

* Tested clang 3.3 and clang 3.4 on Travis CI

* Tested locally on Mac OS 10.9.2, Xcode 5.1

* The issue was rooted in `AC_PROG_CXX(clang++ g++)` and the order of compiler setup.
  The x$GCC variable was so that flags were prepend to CXXFLAGS, some are unknown to Clang.
  Reordering the compiler tests and setting them properly seems to eliminate the issue.