globalRegMaybe inconsistencies on aarch64

CmmSink claims in one place globalRegMaybe isn't available on ARM:

isTrivial :: Platform -> CmmExpr -> Bool
isTrivial _ (CmmReg (CmmLocal _)) = True
isTrivial platform (CmmReg (CmmGlobal (GlobalRegUse r _))) = -- see Note [Inline GlobalRegs?]
  if isARM (platformArch platform)
  then True -- CodeGen.Platform.ARM does not have globalRegMaybe
  else isJust (globalRegMaybe platform r)
  -- GlobalRegs that are loads from BaseReg are not trivial
isTrivial _ (CmmLit _) = True
isTrivial _ _          = False

However CmmSink also has unguarded calls to globalRegMaybe which should be reachable on ARM in the conflicts function:

  -- (6) suspendThread clobbers every global register not backed by a real
  -- register. It also clobbers heap and stack but this is handled by (5)
  | CmmUnsafeForeignCall (PrimTarget MO_SuspendThread) _ _ <- node
  , foldRegsUsed platform (\b g -> globalRegMaybe platform g == Nothing || b) False rhs
  = True

So if this were true I would expect this to fail.

Indeed in CodeGen.Platform.h we have:

globalRegMaybe :: GlobalReg -> Maybe RealReg
#if defined(MACHREGS_i386) || defined(MACHREGS_x86_64) \
    || defined(MACHREGS_powerpc) \
    || defined(MACHREGS_arm) || defined(MACHREGS_aarch64) \
    || defined(MACHREGS_s390x) || defined(MACHREGS_riscv64) \
    || defined(MACHREGS_wasm32) \
    || defined(MACHREGS_loongarch64)

# if defined(REG_Base)
globalRegMaybe BaseReg                  = Just (RealRegSingle REG_Base)
# endif
# if defined(REG_R1)
globalRegMaybe (VanillaReg 1)           = Just (RealRegSingle REG_R1)
# endif
# if defined(REG_R2)
globalRegMaybe (VanillaReg 2)           = Just (RealRegSingle REG_R2)
# endif
...

Which should work for aarch64 just fine. So I think this is no longer the case and the special casing can be removed.