[clang] [llvm] [clang][driver] Set TLSDESC as the default for Android on RISC-V (PR #81198)

[via cfe-commits]

enh-google wrote:

i think my suggestion would be instead of
```
    return isAndroid() && (!isAndroidVersionLT(29) || isRISCV64());
```
just go with
```
    return isAndroid() && isRISCV64();
```

that solves today's problem, and we can worry about arm64 later[1]. (and x86-64 if/when that's implemented. and 32-bit never.)

____
1. why, when arm64 tlsdesc already shipped, and rv64 hasn't shipped yet? for _exactly_ that reason :-) with rv64 i don't even have to [have rprichard] think about app compat issues, say, or [have danalbert] think about communicating the change to ndk users, etc...

https://github.com/llvm/llvm-project/pull/81198