[clang][ARM] re-use arm::isHardTPSupported for hardware TLS check

[nickdesaulniers]

Summary

This conditional check for -mstack-protector-guard=tls got out of sync
with the conditional check for -mtp=cp15 by me in D114116, because I
forgot about the similar check added in D113026.

Re-use the code in arm::isHardTPSupported so that these aren't out of
sync.

Interestingly, our CI reported this when testing
-mstack-protector-guard=tls; it was only reproducible with Debian's LLVM
and not upstream LLVM due to this out of tree patch:
https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/blob/snapshot/debian/patches/930008-arm.diff

Fixes: https://github.com/ClangBuiltLinux/linux/issues/1502

[nickdesaulniers]

clang/lib/Driver/ToolChains/Clang.cpp

3219–3226

If I refactor arm::getReadTPMode a little, we might just be able to use that. Let me see if I can make that work like I'm imagining.

[nickdesaulniers]

clang/lib/Driver/ToolChains/Clang.cpp

3219–3226

eh, now that I've tried that, I think this approach is cleaner as is. Sorry for the noise.

[nickdesaulniers]

clang/lib/Driver/ToolChains/Clang.cpp

3219–3226

https://gist.github.com/nickdesaulniers/402fd60842dafdbc89d43d4e4c3099ee for the other approach I was considering.

clang/lib/Driver/ToolChains/Clang.cpp

if (Arg *A = Args.getLastArg(options::OPT_mstack_protector_guard_EQ)) {
     }
     if ((EffectiveTriple.isARM() || EffectiveTriple.isThumb()) &&
         Value == "tls") {
       if (!Args.hasArg(options::OPT_mstack_protector_guard_offset_EQ)) {
         D.Diag(diag::err_drv_ssp_missing_offset_argument)
             << A->getAsString(Args);
         return;
       }
       // Check whether the target subarch supports the hardware TLS register
-      if (arm::getARMSubArchVersionNumber(EffectiveTriple) < 7 &&
-          llvm::ARM::parseArch(EffectiveTriple.getArchName()) !=
-              llvm::ARM::ArchKind::ARMV6T2) {
+      if (!arm::isHardTPSupported(EffectiveTriple)) {
         D.Diag(diag::err_target_unsupported_tp_hard)
             << EffectiveTriple.getArchName();
         return;
       }
       // Check whether the user asked for something other than -mtp=cp15
       if (Arg *A = Args.getLastArg(options::OPT_mtp_mode_EQ)) {
         StringRef Value = A->getValue();
         if (Value != "cp15") {
           D.Diag(diag::err_drv_argument_not_allowed_with)
               << A->getAsString(Args) << "-mstack-protector-guard=tls";
           return;
         }
       }
       CmdArgs.push_back("-target-feature");