libm: Reenable shr_u256_overflow on ppc64le

The tests passes successfully for me on powerpc64le-unknown-linux-gnu
with nightly 1.95.

Author: Gelbpunkt

libm/src/math/support/big/tests.rs

@@ -261,8 +261,6 @@ fn shr_u256() {
 #[test]
 #[should_panic]
 #[cfg(debug_assertions)]
-// FIXME(ppc): ppc64le seems to have issues with `should_panic` tests.
-#[cfg(not(all(target_arch = "powerpc64", target_endian = "little")))]
 fn shr_u256_overflow() {
     // Like regular shr, panic on overflow with debug assertions
     let _ = u256::MAX >> 256;