build: IS_TTY is now set according to GNU Make's MAKE_TERMOUT

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Fixes: FS#2086
The logic for IS_TTY was broken, because it was testing stdin
instead of stdout.
MAKE_TERMOUT was introduced in GNU Make version 4.1 (05 Oct 2014),
so it should be available everywhere nowadays.

Signed-off-by: R. Diez <rdiezmail-openwrt@yahoo.com>

diff --git a/include/toplevel.mk b/include/toplevel.mk
index 744695b19c9fc8f899f197392ebe2abb11ae6a76..48ea44aa2480ad2d80ca1dc2d45cf8a8193a109d 100644 (file)
--- a/include/toplevel.mk
+++ b/include/toplevel.mk
@@ -4,7 +4,7 @@
 
 PREP_MK= OPENWRT_BUILD= QUIET=0
 
-export IS_TTY=$(shell tty -s && echo 1 || echo 0)
+export IS_TTY=$(if $(MAKE_TERMOUT),1,0)
 
 include $(TOPDIR)/include/verbose.mk