Fix gcc.dg/ia64-sync-5.c for architectures with unsigned char as default (PR 96519)

Fix gcc.dg/ia64-sync-5.c for architectures with unsigned char as default (PR 96519)

If char is unsigned, then comparisons of the char array elements against
negative integers in the test will fail as values in the array will always
be positive, and will remain so when promoted to signed int.

2020-08-12  Kwok Cheung Yeung  <kcy@codesourcery.com>

	PR testsuite/96519

	gcc/testsuite/
	* gcc.dg/ia64-sync-5.c (AC, init_qi, test_qi): Change element type to
	signed char.