revert broken kernel Makefile modification

see [1] for upstream report

1: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1758856/comments/1
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

patches/kernel/0007-Revert-UBUNTU-Packaging-retpoline-add-safe-usage-hin.patch

@@ -0,0 +1,56 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Fabian=20Gr=C3=BCnbichler?= <f.gruenbichler@proxmox.com>
+Date: Tue, 3 Apr 2018 14:59:26 +0200
+Subject: [PATCH] Revert "UBUNTU: [Packaging] retpoline -- add safe usage hint
+ support"
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+This (partially) reverts commit 1e39020902132b3065bedf0a0c33031e89f9f57a.
+
+this modifies the upstream kernel build to call an Ubuntu script which
+we remove before building. it would also be required by any module
+builds afterwards and is not shipped by Ubuntu's kernel packages either.
+
+Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
+---
+ scripts/Makefile.build | 10 +---------
+ 1 file changed, 1 insertion(+), 9 deletions(-)
+
+diff --git a/scripts/Makefile.build b/scripts/Makefile.build
+index 9dc3f41f4ff5..36247e983f4b 100644
+--- a/scripts/Makefile.build
++++ b/scripts/Makefile.build
+@@ -297,27 +297,19 @@ objtool_dep = $(objtool_obj)					\
+ 	      $(wildcard include/config/orc/unwinder.h		\
+ 			 include/config/stack/validation.h)
+ 
+-ifdef CONFIG_RETPOLINE
+-cmd_ubuntu_retpoline = $(CONFIG_SHELL) $(srctree)/debian/scripts/retpoline-extract-one $(@) $(<) "$(filter -m16 %code16gcc.h,$(a_flags))";
+-else
+-cmd_ubuntu_retpoline =
+-endif
+-
+ define rule_cc_o_c
+ 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
+ 	$(call cmd_and_fixdep,cc_o_c)					  \
+ 	$(cmd_checkdoc)							  \
+ 	$(call echo-cmd,objtool) $(cmd_objtool)				  \
+ 	$(cmd_modversions_c)						  \
+-	$(call echo-cmd,ubuntu-retpoline) $(cmd_ubuntu_retpoline)	  \
+ 	$(call echo-cmd,record_mcount) $(cmd_record_mcount)
+ endef
+ 
+ define rule_as_o_S
+ 	$(call cmd_and_fixdep,as_o_S)					  \
+ 	$(call echo-cmd,objtool) $(cmd_objtool)				  \
+-	$(cmd_modversions_S)						  \
+-	$(call echo-cmd,ubuntu-retpoline) $(cmd_ubuntu_retpoline)
++	$(cmd_modversions_S)
+ endef
+ 
+ # List module undefined symbols (or empty line if not enabled)
+-- 
+2.14.2
+