The arch or cpu has its default fpu features and versions such as fpuv2_sf/fpuv3_sf.
And there is also -mfpu option to specify and override fpu version and features.
For example, C860 has fpuv3_sf/fpuv3_df feature as default, when
-mfpu=fpv2 is given, fpuv3_sf/fpuv3_df is replaced with fpuv2_sf/fpuv2_df.
Add CSKY target toolchains to support csky in linux and elf environment.
It can leverage the basic universal Linux toolchain for linux environment, and only add some compile or link parameters.
For elf environment, add a CSKYToolChain to support compile and link.
Also add some parameters into basic codebase of clang driver.
Differential Revision: https://reviews.llvm.org/D121445
Zi Xuan Wu (Zeson)