Fix signed integer overflow in data-streamer.c

Running the testsuite with a -fsanitize=undefined instrumented compiler
shows:
 % gcc -O2 -flto -fno-use-linker-plugin -flto-partition=none testsuite/gcc.dg/torture/pr28045.c
gcc/data-streamer.c:113:45: runtime error: negation of -9223372036854775808 cannot be represented in type 'long int'; cast to an unsigned type to negate this value to itself

The fix is obvious.

From-SVN: r215706

gcc/ChangeLog

+2014-09-30  Markus Trippelsdorf  <markus@trippelsdorf.de>
+
+	* data-streamer.c (bp_unpack_var_len_int): Avoid signed
+	integer overflow.
+
 2014-09-29  Andi Kleen  <ak@linux.intel.com>
 
 	* opts.c (print_filtered_help): Print --param min/max/default

gcc/data-streamer.c

@@ -110,7 +110,7 @@ bp_unpack_var_len_int (struct bitpack_d *bp)
       if ((half_byte & 0x8) == 0)
 	{
 	  if ((shift < HOST_BITS_PER_WIDE_INT) && (half_byte & 0x4))
-	    result |= - ((HOST_WIDE_INT)1 << shift);
+	    result |= - (HOST_WIDE_INT_1U << shift);
 
 	  return result;
 	}