[sanitizers] Move "Prepare" step before "Info" and fix venv path

Moving "Prepare" before "Info" allows the "Info" step to report the
correct python version from the virtual environment.

Also fixes the venv directory name to use an underscore (`llvm_venv`)
consistently and ensures it is excluded from clobbering.

Author: vitalybuka

zorg/buildbot/builders/sanitizers/buildbot_functions.sh

@@ -46,6 +46,23 @@ function include_config() {
 
 include_config
 
+build_step "Prepare"
+
+export LIT_OPTS="--time-tests"
+
+{
+  [[ -f llvm_venv/bin/activate ]] || python3 -m venv llvm_venv
+  . llvm_venv/bin/activate
+  pip install --upgrade pip
+  pip install psutil pyyaml Pygments
+
+  CMAKE_COMMON_OPTIONS+=" -DPython3_EXECUTABLE=$(which python)"
+} || build_exception
+
+LIT_OPTS+=" --timeout=900"
+
+CMAKE="$(which cmake)"
+
 build_step "Info"
 (
   set +e
@@ -65,6 +82,9 @@ build_step "Info"
   echo
   cmake --version
   echo
+  which python
+  python --version
+  echo
   uname -a
   echo
   ldd --version
@@ -76,25 +96,6 @@ build_step "Info"
   hostname -f
 )
 
-build_step "Prepare"
-
-
-export LIT_OPTS="--time-tests"
-
-{
-  [[ -f llvm-venv/bin/activate ]] || python3 -m venv llvm-venv
-  . llvm-venv/bin/activate
-  pip install --upgrade pip
-  pip install psutil pyyaml Pygments
-
-  $ROOT/llvm-venv/bin/python --version
-  CMAKE_COMMON_OPTIONS+=" -DPython3_EXECUTABLE=$ROOT/llvm-venv/bin/python"
-} || build_exception
-
-LIT_OPTS+=" --timeout=900"
-
-CMAKE="$(which cmake)"
-
 function cmake() {
   (
     set -x
@@ -126,7 +127,7 @@ function clobber {
       exit 1
     fi
     # Keep sources in ./llvm-project and ./llvm_build0 for faster builds.
-    find . -maxdepth 1 -mindepth 1 -path ./llvm-project -prune -o -path ./llvm_build0 -prune -o -print -exec rm -rf {} \;
+    find . -maxdepth 1 -mindepth 1 -path ./llvm-project -prune -o -path ./llvm_build0 -prune -o -path ./llvm_venv -prune -o -print -exec rm -rf {} \;
     du -hs ./* | sort -h
     return 0
   else