Possibly fix configuration test on AIX.

Modules/CheckCXXCompilerFlag.cmake

@@ -33,6 +33,7 @@ MACRO (CHECK_CXX_COMPILER_FLAG _FLAG _RESULT)
      FAIL_REGEX "[Uu]nknown option"                         # HP
      FAIL_REGEX "[Ww]arning: [Oo]ption"                     # SunPro
      FAIL_REGEX "command option .* is not recognized"       # XL
+     FAIL_REGEX "not supported in this configuration; ignored"       # AIX
      )
    SET (CMAKE_REQUIRED_DEFINITIONS "${SAFE_CMAKE_REQUIRED_DEFINITIONS}")
 ENDMACRO (CHECK_CXX_COMPILER_FLAG)