test-release.sh: Only build clang for stage1 and stage2

[tstellar]

Summary

The stage1 and stage2 builds aren't packaged, so we only need to build
enough of the toolchain to build the next phase.

[thieta]

I think we should include lld as well - now that LLD can produce production binaries on all platforms I think it makes sense to prefer that over system linker.

When we discussed this earlier I think we talked about only running the tests at the end the product. I still think it makes sense to not do the full testing in Phase 1/2, but other people can disagree with that if we think it will not catch issues.

[tstellar]

In D141552#4047517, @thieta wrote:

I think we should include lld as well - now that LLD can produce production binaries on all platforms I think it makes sense to prefer that over system linker.

I think in addition to building lld, we would also have to add another cmake flag like -DLLVM_USE_LLD when configuring. That might be worthy a separate change, since it will change the final output (whereas this current change does not affect the final output at all).

When we discussed this earlier I think we talked about only running the tests at the end the product. I still think it makes sense to not do the full testing in Phase 1/2, but other people can disagree with that if we think it will not catch issues.

It doesn't look like the tests currently run for stage 1 and stage 2.

[thieta]

Good plan. Let's merge this and we can do another with lld later.

[amyk]

I think this LGTM as well.

llvm/utils/release/test-release.sh

case $Flavor in
             ;;
         * )
             echo "# Invalid flavor '$Flavor'"
             echo ""
             return
             ;;
     esac
 
+    if [ "$Phase" -eq "3" ]; then
       project_list=${projects// /;}
       # Leading spaces will result in ";<runtime name>". This causes a CMake
       # error because the empty string before the first ';' is treated as an
       # unknown runtime name.
       runtimes=$(echo $runtimes | sed -e 's/^\s*//')
       runtime_list=${runtimes// /;}
+    else
+      project_list="clang"
+      runtime_list=""
+    fi
     echo "# Using C compiler: $c_compiler"
     echo "# Using C++ compiler: $cxx_compiler"
 
     cd $ObjDir
     echo "# Configuring llvm $Release-$RC $Flavor"
 
     echo "#" env CC="$c_compiler" CXX="$cxx_compiler" \
         cmake -G "$generator" \