[llvm] [X86] Fix an assembler bug of CMPCCXADD. (PR #66748)

[Freddy Ye via llvm-commits]

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@@ -768,3 +768,6 @@
 // CHECK: encoding: [0xc4,0x62,0xa9,0xe4,0x8a,0x00,0xfc,0xff,0xff]
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FreddyLeaf wrote:

// CHECK: cmpsxadd  %r10, %r9, 268435456(%rbp,%r14,8)
It happens `%r10 ` `wrongly` set the R bit. So I added a test of `%ecx, %r8d, (%rip)`

https://github.com/llvm/llvm-project/pull/66748