Makefile: fix processing of default environment file

Allow the default environment file to contain long lines split into
multiples lines.

Leading white spaces can be added for readability as well.

Signed-off-by: Samuel Mescoff <samuel@mescoff.fr>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/Makefile b/Makefile
index 55aa90c..07539ca 100644
--- a/Makefile
+++ b/Makefile
@@ -1830,7 +1830,7 @@
 	(grep -v '^#' | \
 	 grep -v '^$$' | \
 	 tr '\n' '\0' | \
-	 sed -e 's/\\\x0/\n/g' | \
+	 sed -e 's/\\\x0\s*//g' | \
 	 xxd -i ; echo ", 0x00" ; )
 endef