[clang] [llvm] [PowerPC] _Float16 scalar datatype support for Power8+ (PR #196559)

[Tony Varghese via cfe-commits]

tonykuttai wrote:

Updated the PR. rebased onto current main, review feedback addressed. 
The convention implemented here (scalar _Float16 in FPRs, native 16-bit format) is still under discussion internally. It matches GCC's in-flight implementation (Michael Meissner's _Float16 series on gcc-patches). This is still an experimental PR now which we should be merged **only after the ABI is finalized for the PowerPC targets**.

https://github.com/llvm/llvm-project/pull/196559