[RISCV] Handle fcopysign(f32, f64) and fcopysign(f64, f32)
Summary: Adds tablegen patterns to explicitly handle fcopysign where
the magnitude and sign arguments have different types, due to the
sign value casts being removed the by DAGCombiner. Support for RV32IF
follows in a separate commit. Adds tests for all relevant scenarios
except RV32IF.
Reviewers: lenary
Reviewed By: lenary
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70678
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC after: 1 week
X-MFC-With: r353358
2b2a17f472