[X86][KCFI] Do not require linux triple for kcfi-arity

This code doesn't assume the Linux ABI, but the standard x86-64
SysV ABI, which is used (with minor variations) by all non-Windows
targets.

Requiring "linux" as the OS here is problematic, because the actual
OS (as opposed to users of the OS) is generally compiled against the
"none" target.

Author: nikic

llvm/lib/Target/X86/X86AsmPrinter.cpp

@@ -192,9 +192,9 @@ void X86AsmPrinter::emitKCFITypeId(const MachineFunction &MF) {
   unsigned DestReg = X86::EAX;
 
   if (F.getParent()->getModuleFlag("kcfi-arity")) {
-    // The ArityToRegMap assumes the 64-bit Linux kernel ABI
+    // The ArityToRegMap assumes the 64-bit SysV ABI.
     [[maybe_unused]] const auto &Triple = MF.getTarget().getTargetTriple();
-    assert(Triple.isArch64Bit() && Triple.isOSLinux());
+    assert(Triple.isArch64Bit() && !Triple.isOSWindows());
 
     // Determine the function's arity (i.e., the number of arguments) at the ABI
     // level by counting the number of parameters that are passed

llvm/test/CodeGen/X86/kcfi-arity.ll

@@ -1,4 +1,5 @@
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -verify-machineinstrs < %s | FileCheck %s --check-prefix=ASM
+; RUN: llc -mtriple=x86_64-unknown-none -verify-machineinstrs < %s | FileCheck %s --check-prefix=ASM
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -verify-machineinstrs -stop-after=finalize-isel < %s | FileCheck %s --check-prefixes=MIR,ISEL
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -verify-machineinstrs -stop-after=kcfi < %s | FileCheck %s --check-prefixes=MIR,KCFI