CPP_LIBRARY has never been used outside configure.ac

...ever since its introduction with f5aa0448
"Enable optionally using libc++ on OS X (when targeting 10.7 or later)"

Change-Id: I26ece69d7a00c7452cd027928c318bbf31d6284b

config_host.mk.in

@@ -69,7 +69,6 @@ export COMMONS_LOGGING_VERSION=@COMMONS_LOGGING_VERSION@
 export COMPATH=@COMPATH@
 export COMPILER_PLUGINS=@COMPILER_PLUGINS@
 export COM_GCC_IS_CLANG=@COM_GCC_IS_CLANG@
-export CPP_LIBRARY=@CPP_LIBRARY@
 export CPPUNIT_CFLAGS=$(gb_SPACE)@CPPUNIT_CFLAGS@
 export CPPUNIT_LIBS=$(gb_SPACE)@CPPUNIT_LIBS@
 export CPUNAME=@CPUNAME@

configure.ac

@@ -6119,7 +6119,6 @@ foo bar
     AC_MSG_ERROR([Could not figure out what C++ library this is]))))
 AC_MSG_RESULT([$cpp_library_name])
 AC_LANG_POP([C++])
-AC_SUBST(CPP_LIBRARY)
 
 dnl ===================================================================
 dnl C++11