Project: Detect other compilers before detecting Clang.

Commit v2.8.10.1~5^2 (Fix PathScale compiler id for Clang-based
upstream, 2012-11-05) re-ordered the detection logic for PathScale.

Other compiler vendors are also producing Clang-based frontends, so
detect "actual" Clang as one of the last compilers to allow for others
doing the same.

    http://llvm.org/devmtg/2014-04/PDFs/Posters/ClangIntel.pdf
    http://docwiki.embarcadero.com/RADStudio/XE5/en/Clang-based_C%2B%2B_Compilers

Modules/CMakeCompilerIdDetection.cmake

@@ -61,8 +61,6 @@ function(compiler_id_detection outvar lang)
     list(APPEND ordered_compilers
       Intel
       PathScale
-      AppleClang
-      Clang
       Embarcadero
       Borland
       Watcom
@@ -84,6 +82,8 @@ function(compiler_id_detection outvar lang)
     endif()
     list(APPEND ordered_compilers
       SCO
+      AppleClang
+      Clang
       GNU
       MSVC
       ADSP