scripts/oe-buildenv-internal: Fix regression in BB_ENV_EXTRAWHITE setting

The commit OE-Core:ada4639 (oe-buildenv-internal: simplify derivation
of BB_ENV_EXTRAWHITE) changed the format of BB_ENV_EXTRAWHITE
variable to:

,----
| BB_ENV_EXTRAWHITE='ALL_PROXY
| BB_NO_NETWORK
| BB_NUMBER_THREADS
| ...
| '
`----

Instead of:

,----
| BB_ENV_EXTRAWHITE='ALL_PROXY BB_NO_NETWORK BB_NUMBER_THREADS...'
`----

The old format allow for external script parsing easier and there is
no need to change the format as it has no benefit from usage
perspective.

(From OE-Core rev: 773e9ef9bacbf1e63fe758915d599d11762b8c1f)

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-buildenv-internal

@@ -116,6 +116,6 @@ all_proxy NO_PROXY no_proxy SSH_AGENT_PID SSH_AUTH_SOCK BB_SRCREV_POLICY \
 SDKMACHINE BB_NUMBER_THREADS BB_NO_NETWORK PARALLEL_MAKE GIT_PROXY_COMMAND \
 SOCKS5_PASSWD SOCKS5_USER SCREENDIR STAMPS_DIR"
 
-BB_ENV_EXTRAWHITE=$(echo $BB_ENV_EXTRAWHITE $BB_ENV_EXTRAWHITE_OE | sed 's/ /\n/g' | LC_ALL=C sort --unique)
+BB_ENV_EXTRAWHITE="$(echo $BB_ENV_EXTRAWHITE $BB_ENV_EXTRAWHITE_OE | tr ' ' '\n' | LC_ALL=C sort --unique | tr '\n' ' ')"
 
 export BB_ENV_EXTRAWHITE