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.

src/types.c

@@ -44,6 +44,17 @@ const ffi_type ffi_type_##name = {		\
   id, NULL					\
 }
 
+#define FFI_NONCONST_TYPEDEF(name, type, id)	\
+struct struct_align_##name {			\
+  char c;					\
+  type x;					\
+};						\
+ffi_type ffi_type_##name = {			\
+  sizeof(type),					\
+  offsetof(struct struct_align_##name, x),	\
+  id, NULL					\
+}
+
 /* Size and alignment are fake here. They must not be 0. */
 const ffi_type ffi_type_void = {
   1, 1, FFI_TYPE_VOID, NULL
@@ -73,5 +84,9 @@ FFI_TYPEDEF(double, double, FFI_TYPE_DOUBLE);
 # endif
 const ffi_type ffi_type_longdouble = { 16, 16, 4, NULL };
 #elif FFI_TYPE_LONGDOUBLE != FFI_TYPE_DOUBLE
+# if HAVE_LONG_DOUBLE_VARIANT
+FFI_NONCONST_TYPEDEF(longdouble, long double, FFI_TYPE_LONGDOUBLE);
+# else
 FFI_TYPEDEF(longdouble, long double, FFI_TYPE_LONGDOUBLE);
+# endif
 #endif