Simplify build-time config checks.

These now simply reflect whatever config.hpp reports, and are therefore always in synch with the headers.
They are also now compile-time tests only, which means they function with cross compilers.
Fixes: https://svn.boost.org/trac/boost/ticket/12805.

test/all/Jamfile.v2

@@ -1,7 +1,7 @@
 #
 # Regression test Jamfile for boost configuration setup.
 # *** DO NOT EDIT THIS FILE BY HAND ***
-# This file was automatically generated on Sun Feb  5 19:09:22 2017
+# This file was automatically generated on Mon Apr 17 12:45:44 2017
 #  by libs/config/tools/generate.cpp
 # Copyright John Maddock.
 # Use, modification and distribution are subject to the