Update metadata for "kbuild: Do not use hyphen in exported variable name"

I updated the commit message and re-submitted it after further
investigation.

debian/patches/bugfix/all/kbuild-do-not-use-hyphen-in-exported-variable-name.patch

@@ -1,17 +1,18 @@
 From: Ben Hutchings <ben@decadent.org.uk>
-Date: Fri, 26 Aug 2016 01:31:28 +0100
+Date: Sat, 19 Aug 2017 21:37:18 +0100
 Subject: kbuild: Do not use hyphen in exported variable name
 Bug-Debian: https://bugs.debian.org/833561
-Forwarded: https://marc.info/?l=linux-kbuild&m=141523555023625
+Forwarded: https://marc.info/?l=linux-kbuild&m=150317820622984&w=2
 
 This definition in Makefile.dtbinst:
 
     export dtbinst-root ?= $(obj)
 
 should define and export dtbinst-root when handling the root dts
-directory, and do nothing in the subdirectories.  However, the
-variable does not reliably get exported to the environment, perhaps
-because its name contains a hyphen.
+directory, and do nothing in the subdirectories.  However some shells,
+including dash, will not pass through environment variables whose name
+includes a hyphen.  Usually GNU make does not use a shell to recurse,
+but if e.g. $(srctree) contains '~' it will use a shell here.
 
 Rename the variable to dtbinst_root.
 
@@ -19,6 +20,11 @@ References: https://bugs.debian.org/833561
 Fixes: 323a028d39cdi ("dts, kbuild: Implement support for dtb vendor subdirs")
 Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
 ---
+ scripts/Makefile.dtbinst | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/scripts/Makefile.dtbinst b/scripts/Makefile.dtbinst
+index 34614a48b717..993fb85982df 100644
 --- a/scripts/Makefile.dtbinst
 +++ b/scripts/Makefile.dtbinst
 @@ -14,7 +14,7 @@ src := $(obj)