Testsuite, i386: mark test as requiring dfp

Test currently fails on darwin with:
error: decimal floating-point not supported for this target

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr112445.c: Require dfp.

gcc/testsuite/gcc.target/i386/pr112445.c

 /* { dg-do compile { target int128 } } */
+/* { dg-require-effective-target dfp } */
 /* { dg-options "-O -march=cascadelake -fwrapv" } */
 
 typedef _Decimal64 d64;