While implementing unwind information using UnwindAssemblyInstEmulation I ran

into some cleanup I have been wanting to do when reading/writing registers.
Previously all RegisterContext subclasses would need to implement:

virtual bool
ReadRegisterBytes (uint32_t reg, DataExtractor &data);

virtual bool
WriteRegisterBytes (uint32_t reg, DataExtractor &data, uint32_t data_offset = 0);

There is now a new class specifically designed to hold register values: 
        lldb_private::RegisterValue
        
The new register context calls that subclasses must implement are:

virtual bool
ReadRegister (const RegisterInfo *reg_info, RegisterValue &reg_value) = 0;

virtual bool
WriteRegister (const RegisterInfo *reg_info, const RegisterValue &reg_value) = 0;

The RegisterValue class must be big enough to handle any register value. The
class contains an enumeration for the value type, and then a union for the 
data value. Any integer/float values are stored directly in an appropriate
host integer/float. Anything bigger is stored in a byte buffer that has a length
and byte order. The RegisterValue class also knows how to copy register value
bytes into in a buffer with a specified byte order which can be used to write
the register value down into memory, and this does the right thing when not
all bytes from the register values are needed (getting a uint8 from a uint32
register value..). 

All RegiterContext and other sources have been switched over to using the new
regiter value class.

llvm-svn: 131096