m2: Remove uses of {FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE

Joseph pointed out "floating types should have their mode,
not a poorly defined precision value" in the discussion[1],
as he and Richi suggested, the existing macros
{FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE will be replaced with a
hook mode_for_floating_type.  To be prepared for that, this
patch is to remove uses of {FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE
in m2.  Currently they are used for assertion and can be
replaced with TYPE_SIZE check on the corresponding type node,
since we dropped the call to layout_type which would early
return once TYPE_SIZE is set and this assertion ensures it's
safe to drop that call.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2024-May/651209.html

gcc/m2/ChangeLog:

	* gm2-gcc/m2type.cc (build_m2_short_real_node): Adjust assertion with
	TYPE_SIZE check.
	(build_m2_real_node): Likewise.
	(build_m2_long_real_node): Add assertion with TYPE_SIZE check.

gcc/m2/gm2-gcc/m2type.cc

@@ -1416,28 +1416,29 @@ static tree
 build_m2_short_real_node (void)
 {
   /* Define `SHORTREAL'.  */
-  ASSERT_CONDITION (TYPE_PRECISION (float_type_node) == FLOAT_TYPE_SIZE);
+  ASSERT_CONDITION (TYPE_SIZE (float_type_node));
   return float_type_node;
 }
 
 static tree
 build_m2_real_node (void)
 {
   /* Define `REAL'.  */
-  ASSERT_CONDITION (TYPE_PRECISION (double_type_node) == DOUBLE_TYPE_SIZE);  
+  ASSERT_CONDITION (TYPE_SIZE (double_type_node));
   return double_type_node;
 }
 
 static tree
 build_m2_long_real_node (void)
 {
   tree longreal;
-  
+
   /* Define `LONGREAL'.  */
   if (M2Options_GetIEEELongDouble ())
     longreal = float128_type_node;
   else
     longreal = long_double_type_node;
+  ASSERT_CONDITION (TYPE_SIZE (longreal));
   return longreal;
 }