The PR adds the support of CoreDump debugging for RISC-V 64. It
implements new `RegisterContextCorePOSIX_riscv64` class.
Also, the contribution fixes `GetRegisterCount()` ->
`GetRegisterSetCount()` misprint in
`RegisterContextPOSIX_riscv64::GetRegisterSetCount()` method, which
leaded to `set && "Register set should be valid."` assertion during
`register info aX` command call.
The patch was tested (on coredumps generated for simple Integer/FP
calculation code) for _cross x86_64 -> RISCV_ and _native RISCV_ LLDB
builds. There were performed basic LLDB functionality tests, such as:
- CoreDump file load
- Backtrace / frames
- GP/FP registers read/info/list
- Basic switch between threads
- Disassembler code
- Memory regions read / display
d3a9043ec2