[NFC][PowerPC] Marked the addr-label.ll test unsupported on PowerPC.

The addr-label.ll test uses the following setup:

define ptr @test1() nounwind {
entry:
	ret ptr blockaddress(@test1b, %test_label)
}

define i32 @test1b() nounwind {
entry:
	ret i32 -1
test_label:
	br label %ret
ret:
	ret i32 -1
}

However, according to the LLVM Reference guide for blockaddress()
"This value only has defined behavior when used as an operand to the
‘indirectbr’ or for comparisons against null." For this test the value
is just returned as a pointer from test1().

On PowerPC this test has unreliable results as the order in which
passes are run can make this test pass or fail. If the %test_label
in test1b() is removed before a number of passes are completed on
test1() then this test will fail on PowerPC.

I have marked this test as UNSUPPORTED on PowerPC.