JIT: Unnecessary GC transitions recorded for tailcalls

[jakobbotsch]

The logic in emitIns_Call removes callee-trashed registers from the saved set recorded:

runtime/src/coreclr/jit/emitxarch.cpp

Lines 11174 to 11177 in 8cb57ab

	// Trim out any callee-trashed registers from the live set.
	regMaskTP savedSet = emitGetGCRegsSavedOrModified(params.methHnd);
	regMaskTP gcrefRegs = params.gcrefRegs & savedSet;
	regMaskTP byrefRegs = params.byrefRegs & savedSet;

For jumps this does not really make sense. We should be able to avoid some unnecessary GC transitions by avoiding changing the gcref regs/byref regs when params.isJump.

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[jakobbotsch]

Noticed this while looking at recording proper GC info for the trampolines in #120303. Those are emitted via emitIns_Call with params.isJump = true, and currently the trampolines end up as

G_M53658_IG12:        ; bbWeight=1, gcrefRegs=0002 {rcx}, byrefRegs=0004 {rdx}, byref
                            ; gcrRegs +[rcx]
                            ; byrRegs +[rdx]
       jmp      (dynamicClass):IL_STUB_AsyncResume_Foo_Tier0(System.Object,byref):System.Object
                            ; gcrRegs -[rcx]
                            ; byrRegs -[rdx]
                                                ;; size=5 bbWeight=1 PerfScore 2.00
G_M53658_IG13:        ; bbWeight=1, gcrefRegs=0002 {rcx}, byrefRegs=0004 {rdx}, byref
                            ; gcrRegs +[rcx]
                            ; byrRegs +[rdx]
       jmp      (dynamicClass):IL_STUB_AsyncResume_Foo_Tier0(System.Object,byref):System.Object
                            ; gcrRegs -[rcx]
                            ; byrRegs -[rdx]
                                                ;; size=5 bbWeight=1 PerfScore 2.00

with multiple superfluous recorded GC info transitions.