Use HAVE_INT128 instead of __SIZEOF_INT128__

Make sure that the configure decision on 128-bit is consistent during
compilation.

Also move uint128_t definition.

riscv/decode.h

@@ -19,11 +19,6 @@ typedef int64_t sreg_t;
 typedef uint64_t reg_t;
 typedef float128_t freg_t;
 
-#ifdef __SIZEOF_INT128__
-typedef __int128 int128_t;
-typedef unsigned __int128 uint128_t;
-#endif
-
 const int NXPR = 32;
 const int NFPR = 32;
 const int NVPR = 32;

riscv/decode_macros.h

@@ -10,6 +10,11 @@
 #include "softfloat_types.h"
 #include "specialize.h"
 
+#ifdef HAVE_INT128
+typedef __int128 int128_t;
+typedef unsigned __int128 uint128_t;
+#endif
+
 // helpful macros, etc
 #define MMU (*p->get_mmu())
 #define STATE (*p->get_state())

riscv/processor.cc

@@ -42,7 +42,7 @@ processor_t::processor_t(const isa_parser_t *isa, const cfg_t *cfg,
   VU.p = this;
   TM.proc = this;
 
-#ifndef __SIZEOF_INT128__
+#ifndef HAVE_INT128
   if (extension_enabled('V')) {
     fprintf(stderr, "V extension is not supported on platforms without __int128 type\n");
     abort();