[source] rules.mk: export TMPDIR

[LEDE Commits]

jow pushed a commit to source.git, branch master:
https://git.lede-project.org/72051f70368b53afa3305e1485c62b7e47fc1210

commit 72051f70368b53afa3305e1485c62b7e47fc1210
Author: Jo-Philipp Wich <jo at mein.io>
AuthorDate: Tue Dec 12 16:28:04 2017 +0100

    rules.mk: export TMPDIR
    
    Set TMPDIR to the same value as the existing TMP_DIR variable in order to
    let gcc and various other utilities use the local temporary directory
    instead of the system-wide one.
    
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 rules.mk | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rules.mk b/rules.mk
index ed796a5..3558f2f 100644
--- a/rules.mk
+++ b/rules.mk
@@ -21,6 +21,7 @@ DUMP:=1
 endif
 
 export TMP_DIR:=$(TOPDIR)/tmp
+export TMPDIR:=$(TMP_DIR)
 
 qstrip=$(strip $(subst ",,$(1)))
 #"))