For targets where i32 is not a legal type (e.g. 64-bit RISC-V), LegalizeIntegerTypes must promote the integer operand of ISD::FPOWI. As this is a signed value, this should be sign-extended.
This patch enables all tests in float-intrinsics.ll, as prior to this patch that file couldn't be compiled for RV64 due to an assertion when performing codegen for fpowi.