From 84a7818121047cf6bb23d8bd3c055d09bb033d32 Mon Sep 17 00:00:00 2001
From: Matthias Stecher <matthiasstecher@gmx.de>
Date: Wed, 23 Sep 2020 20:29:47 +0200
Subject: [PATCH] docs: make varaibles environment-aware

There are all overwriting the environment, even the comment states
otherwise. Fixes it.
---
 docs/src/Makefile | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/src/Makefile b/docs/src/Makefile
index 2ecf7a32..ba87d170 100644
--- a/docs/src/Makefile
+++ b/docs/src/Makefile
@@ -2,10 +2,10 @@
 #
 
 # You can set these variables from the command line.
-SPHINXOPTS    =
-SPHINXBUILD   = sphinx-build
-PAPER         =
-BUILDDIR      = ../dist
+SPHINXOPTS   ?=
+SPHINXBUILD  ?= sphinx-build
+PAPER        ?=
+BUILDDIR     ?= ../dist
 # for cache, etc.
 _BUILDDIR     = _build