Driver: implement --dyld-prefix option.

This option is used to select a dynamic loader prefix to be used
at runtime. Currently this is implemented for the Linux toolchain.

Differential Revision: http://llvm-reviews.chandlerc.com/D851

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182744 91177308-0d34-0410-b5e6-96231b3b80d8
Add a SparcV9ABIInfo class for handling the standard SPARC v9 ABI.

- All integer arguments smaller than 64 bits are extended.
- Large structs are passed indirectly, not using 'byval'.
- Structs up to 32 bytes in size are returned in registers.

Some things are not implemented yet:

- EmitVAArg can be implemented in terms of the va_arg instruction.
- When structs are passed in registers, float members require special
  handling because they are passed in the floating point registers.
- Structs are left-aligned when passed in registers. This may require
  padding.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182745 91177308-0d34-0410-b5e6-96231b3b80d8