This separates the 32-bit sysv/linux/bsd code from the 64-bit linux

code, and makes it possible to link code compiled with different
options to those used to compile libffi.  For example, a
-mlong-double-128 libffi can be used with -mlong-double-64 code.

Using the return value area as a place to pass parameters wasn't such
a good idea, causing a failure of cls_ulonglong.c.  I didn't see this
when running the mainline gcc libffi testsuite because that version of
the test is inferior to the upstreamm libffi test.

Using NUM_FPR_ARG_REGISTERS rather than NUM_FPR_ARG_REGISTERS64 meant
that a parameter save area could be allocated before it was strictly
necessary.  Wrong but harmless.  Found when splitting apart ffi.c
into 32-bit and 64-bit support.

fficonfig.h.in

@@ -73,6 +73,9 @@
 /* Define if you have the long double type and it is bigger than a double */
 #undef HAVE_LONG_DOUBLE
 
+/* Define if you support more than one size of the long double type */
+#undef HAVE_LONG_DOUBLE_VARIANT
+
 /* Define to 1 if you have the `memcpy' function. */
 #undef HAVE_MEMCPY
 
@@ -152,6 +155,9 @@
 /* The size of `long double', as computed by sizeof. */
 #undef SIZEOF_LONG_DOUBLE
 
+/* The size of `size_t', as computed by sizeof. */
+#undef SIZEOF_SIZE_T
+
 /* If using the C implementation of alloca, define if you know the
    direction of stack growth for your system; otherwise it will be
    automatically deduced at runtime.