[x] remaining configure.ac options that feed config.h transferred to cmake, except for dependency options. largely tested to replicate libtool and added to upgrade guide.
[x] LIBINT_HOST_ARCH & LIBINT_TARGET_ARCH removed as never used
[x] the LIBINT2_REALTYPE/LIBINT_USER_DEFINED_REAL have a compile-check, and the data transfer seems to hold together, but definitely needs testing with full code. it's only for the C interface?
currently atop #312 . diff of the new stuff: https://github.com/loriab/libint/compare/orderingsconfig...loriab:libint:configconfig
LIBINT_HOST_ARCH&LIBINT_TARGET_ARCHremoved as never usedCXX_ALLOWS_DEFPARAMTEMPLATE_AS_TEMPTEMPPARAMleft undef as there's no libtool check. are cxx_template_template_parameters (c++98) or cxx_default_function_template_args (c++11) relevant from https://cmake.org/cmake/help/v3.26/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html ?