For C compatible variadic dispatch, the compiler now generates two
entrypoints for variadic functions. An entrypoint with specialized
signature that is used for direct C calls from the same file and an
entrypoint with generic signature that implements the variadic to
variadic dispatch, i.e. checking the number of arguments and then
calling the specialized entrypoint.
This approach is faster than using the wrapper functions in
variadic_dispatch_table. The reasons are threefold: we save a call to
ecl_process_env(), we don't need a call through a function pointer but
instead use a direct call to the specialized entrypoint and we emit
better code to deal with required arguments since the number of those
are known.
Moreover, for functions with optional arguments the new approach is
less stack hungry since we can allocate an array of size smaller than
ECL_C_ARGUMENTS_LIMIT to store the arguments.
Many parts of the source code were bent backward to support builds
without long floats which are always present given we depend expect
c99 compiler.
The corresponding C macros (ECL_LONG_FLOAT) and the *feature*
entry (:long-float) are marked as deprecated in the documentation.
