[flang-commits] [flang] [flang] Update instructions for a standalone flang build (PR #68361)

[Pete Steinfeld via flang-commits]

https://github.com/psteinfeld created https://github.com/llvm/llvm-project/pull/68361

I added instructions for setting the environment variable ROOT_DIR.

>From 8c081dead59cc9fe91ecc590b8416d52e15e2e8f Mon Sep 17 00:00:00 2001
From: Peter Steinfeld <psteinfeld at nvidia.com>
Date: Thu, 5 Oct 2023 14:53:45 -0700
Subject: [PATCH] [flang] Update instructions for a standalone flang build

I added instructions for setting the environment variable ROOT_DIR.
---
 flang/docs/GettingStarted.md | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/flang/docs/GettingStarted.md b/flang/docs/GettingStarted.md
index f5319a7c38541fd..3b3f14d4fed1a8c 100644
--- a/flang/docs/GettingStarted.md
+++ b/flang/docs/GettingStarted.md
@@ -141,8 +141,14 @@ code is in good shape.
 
 ### Building flang standalone
 To do the standalone build, start by building flang in tree as described above.
-This build is base build for subsequent standalone builds.  Start each
-standalone build the same way by cloning the source for llvm-project:
+This build can be used as the  base build for several subsequent standalone
+builds.  Set the environment variable **ROOT_DIR** to the directory that
+contains the subdirectory `build` that was created previously, for example:
+```bash
+export ROOTDIR=/home/user/root
+```
+Start each standalone build the same way by cloning the source for
+llvm-project:
 ```bash
 mkdir standalone
 cd standalone
@@ -175,7 +181,7 @@ cmake \
 ninja
 ```
 
-To run the flang tests on this build, execute the command in the "flang/build"
+To run the flang tests on this build, execute the command in the `flang/build`
 directory:
 ```bash
 ninja check-flang