VASM part 2: call, shuffleArgs, shuffle2, syncpoint, vregs

Summary: Converts more emitter-helper code to use VASM, notably shuffleArgs,
prepXMM, and PhysRegSaver. Start using makeReg() to generate temporary
virtual registers instead of named reserved tmps like rAsm/rCgGP/rCgXMM*.

Reviewed By: @alexmalyshev

Differential Revision: D1460362
VASM part 3: calls and other trickyness

Summary: Convert cgCallHelper to vasm. The two interesting parts of this are
catch edges and LdObjMethod. LdObjMethod requires two special vasm
opcodes that support the alignment and patching that goes on.

Catch blocks are supported by an "unwind" instruction that behaves like
a conditional branch; the taken edge represents a transfer of control
from the callee to the unwinder block. The normal edge represents a
normal return.

This diff starts using vasm for service requests. the service request
opcodes encapsulate more or less all of the corresponding emitReqXXX
helper functions, so they generate more asm after register allocation
and sometimes re-enter Vauto recursively. See t4785959.

Reviewed By: @alexmalyshev

Differential Revision: D1460363