Replace --env with --source-dir

Remove the --env argument, which was compulsory for all subcommands, and
replace it with a --source-dir argument, only for those subcommands that
need it.

We do this for 2 reasons:
* Not all subcommands care about the source directory (e.g. llvm.py
  build won't need it)
* llvm.py should not have any knowledge about environments - that
  concept only makes sense for the helper scripts. llvm.py should
  instead receive very specific info about where the source and build
  directories are.

Change-Id: Iffaeef95559e8923bd883d5c51fed8c306287280
diff --git a/helpers/llvm-push b/helpers/llvm-push
index b7ad1d1..6dabc11 100755
--- a/helpers/llvm-push
+++ b/helpers/llvm-push
@@ -16,6 +16,6 @@
 . llvm-common
 verify_env
 repos=$LLVM_ROOT/repos
-env=$(dirname $LLVM_SRC)
+source_dir=$LLVM_SRC
 
-safe_run python3 $llvmtool --env $env push
+safe_run python3 $llvmtool push --source-dir $source_dir