[llvm] Prevent building for riscv32-unknown-fuchsia

[leonardchan]

Summary

Fuchsia is exclusively 64-bit so this throw an error when using this triple.

[phosek]

LGTM

[asb]

A belated LGTM - thank you!

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

: LLVMTargetMachine(T, computeDataLayout(TT), TT, CPU, FS, Options,
                         getEffectiveRelocModel(TT, RM),
                         getEffectiveCodeModel(CM, CodeModel::Small), OL),
       TLOF(std::make_unique<RISCVELFTargetObjectFile>()) {
   initAsmInfo();
 
   // RISC-V supports the MachineOutliner.
   setMachineOutliner(true);
   setSupportsDefaultOutlining(true);
+
+  if (TT.isOSFuchsia() && !TT.isArch64Bit())
+    report_fatal_error("Fuchsia is only supported for 64-bit");
 }
 
 const RISCVSubtarget *
 RISCVTargetMachine::getSubtargetImpl(const Function &F) const {
   Attribute CPUAttr = F.getFnAttribute("target-cpu");
   Attribute TuneAttr = F.getFnAttribute("tune-cpu");
   Attribute FSAttr = F.getFnAttribute("target-features");
 

llvm/test/CodeGen/RISCV/rv32-fuchsia.ll

+; RUN: not --crash llc -mtriple=riscv32-unknown-fuchsia < %s 2>&1 | FileCheck %s
+
+; CHECK: LLVM ERROR: Fuchsia is only supported for 64-bit
+define void @nothing() nounwind {
+  ret void
+}