local.conf.sample: use ?= to assign BB_ENV_EXTRAWHITE variables

Use ?= so that the BB_ENV_EXTRAWHITE variables can be overridden from
the environment.

[YOCTO #4367]

Signed-off-by: Jesse Zhang <sen.zhang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/meta-yocto/conf/local.conf.sample.extended b/meta-yocto/conf/local.conf.sample.extended
index 3dc73fbec6..07e5cf553a 100644
--- a/meta-yocto/conf/local.conf.sample.extended
+++ b/meta-yocto/conf/local.conf.sample.extended
@@ -82,7 +82,7 @@
 # Use "external-MODE" to use the precompiled external toolchains where MODE
 # is the type of external toolchain to use e.g. eabi. You need to ensure 
 # the toolchain you want to use is included in an appropriate layer
-# TCMODE = "external-eabi"
+# TCMODE ?= "external-eabi"
 
 # mklibs library size optimization is more useful to smaller images,
 # and less useful for bigger images. Also mklibs library optimization