• Skip over the testcases that call cbrtl on platforms where LDBL_PREC == 53

(arm, mips, powerpc). This fixes the build on these platforms, based on some
ad hoc tinderbox runs I did a while ago

• Skip cast the arguments to powl as long double so powl properly interprets

those arugments at compile-time when picking the type

Sponsored by: EMC / Isilon Storage Division