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

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

Reviewed By: thieta, amyk

Differential Revision: https://reviews.llvm.org/D141552

Author: tstellar

llvm/utils/release/test-release.sh

@@ -404,12 +404,17 @@ function configure_llvmCore() {
             ;;
     esac
 
-    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// /;}
+    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"