target/tilegx: avoid integer overflow in next_page PC check

If the PC is in the last page of the address space, next_page_start
overflows to 0. Fix it.
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

target/tilegx/translate.c

@@ -2375,7 +2375,7 @@ void gen_intermediate_code(CPUState *cs, struct TranslationBlock *tb)
     DisasContext ctx;
     DisasContext *dc = &ctx;
     uint64_t pc_start = tb->pc;
-    uint64_t next_page_start = (pc_start & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
+    uint64_t page_start = pc_start & TARGET_PAGE_MASK;
     int num_insns = 0;
     int max_insns = tb_cflags(tb) & CF_COUNT_MASK;
 
@@ -2415,7 +2415,7 @@ void gen_intermediate_code(CPUState *cs, struct TranslationBlock *tb)
         }
         dc->pc += TILEGX_BUNDLE_SIZE_IN_BYTES;
         if (num_insns >= max_insns
-            || dc->pc >= next_page_start
+            || (dc->pc - page_start >= TARGET_PAGE_SIZE)
             || tcg_op_buf_full()) {
             /* Ending the TB due to TB size or page boundary.  Set PC.  */
             tcg_gen_movi_tl(cpu_pc, dc->pc);