boot/grub2: fix build race condition

Sometimes buildroot fails with:
../grub-core/kern/emu/hostfs.c:20:10: fatal error: config-util.h: No such file or directory
   20 | #include <config-util.h>
      |          ^~~~~~~~~~~~~~~

Add a patch which fixes the Makefile to correctly generate config-util.h
first.

Note: This re-adds a workaround to avoid re-running autoconf. This has
previously been used to avoid having to run the rather complex build
file generation machinery of GRUB2. See 7e64a050fb ("boot/grub2: Fix
GRUB i386-pc build with Ubuntu gcc"), but now we just need to touch
Makefile.in.

Signed-off-by: Stefan Agner <stefan@agner.ch>
[yann.morin.1998@free.fr:
  - add comment with patch name before hook
  - slightly extend commit log that we only touch Makefile.in
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

boot/grub2/0001-Makefile-Make-grub_fstest.pp-depend-on-config-util.h.patch

@@ -0,0 +1,45 @@
+From bb08b723fa7bc56439c7bc166cff361628e73453 Mon Sep 17 00:00:00 2001
+Message-Id: <bb08b723fa7bc56439c7bc166cff361628e73453.1659683176.git.stefan@agner.ch>
+From: Stefan Agner <stefan@agner.ch>
+Date: Fri, 5 Aug 2022 08:59:52 +0200
+Subject: [PATCH] Makefile: Make grub_fstest.pp depend on config-util.h
+
+Warning: This commit does not apply to the GRUB git repository. This
+patch applies against the release tarballs.
+
+Upstream status: https://lists.gnu.org/archive/html/grub-devel/2022-08/msg00045.html
+Signed-off-by: Stefan Agner <stefan@agner.ch>
+---
+ Makefile.am | 2 +-
+ Makefile.in | 2 +-
+ 2 files changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/Makefile.am b/Makefile.am
+index bf9c1ba..f08cfc0 100644
+--- a/Makefile.am
++++ b/Makefile.am
+@@ -51,7 +51,7 @@ libgrub_a_init.c: libgrub_a_init.lst $(top_srcdir)/geninit.sh
+ CLEANFILES += libgrub_a_init.c
+ 
+ # For grub-fstest
+-grub_fstest.pp: $(grub_fstest_SOURCES)
++grub_fstest.pp: config-util.h $(grub_fstest_SOURCES)
+ 	$(CPP) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(grub_fstest_CPPFLAGS) $(CPPFLAGS) \
+ 	  -D'GRUB_MOD_INIT(x)=@MARKER@x@' $^ > $@ || (rm -f $@; exit 1)
+ CLEANFILES += grub_fstest.pp
+diff --git a/Makefile.in b/Makefile.in
+index 13f2eef..2c1d20b 100644
+--- a/Makefile.in
++++ b/Makefile.in
+@@ -13312,7 +13312,7 @@ libgrub_a_init.c: libgrub_a_init.lst $(top_srcdir)/geninit.sh
+ 	sh $(top_srcdir)/geninit.sh `cat $<` > $@ || (rm -f $@; exit 1)
+ 
+ # For grub-fstest
+-grub_fstest.pp: $(grub_fstest_SOURCES)
++grub_fstest.pp: config-util.h $(grub_fstest_SOURCES)
+ 	$(CPP) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(grub_fstest_CPPFLAGS) $(CPPFLAGS) \
+ 	  -D'GRUB_MOD_INIT(x)=@MARKER@x@' $^ > $@ || (rm -f $@; exit 1)
+ 
+-- 
+2.37.1
+

boot/grub2/grub2.mk

@@ -13,6 +13,13 @@ GRUB2_DEPENDENCIES = host-bison host-flex host-grub2
 HOST_GRUB2_DEPENDENCIES = host-bison host-flex
 GRUB2_INSTALL_IMAGES = YES
 
+# 0001-Makefile-Make-grub_fstest.pp-depend-on-config-util.h.patch
+define GRUB2_AVOID_AUTORECONF
+	$(Q)touch $(@D)/Makefile.in
+endef
+GRUB2_POST_PATCH_HOOKS += GRUB2_AVOID_AUTORECONF
+HOST_GRUB2_POST_PATCH_HOOKS += GRUB2_AVOID_AUTORECONF
+
 # CVE-2019-14865 is about a flaw in the grub2-set-bootflag tool, which
 # doesn't exist upstream, but is added by the Redhat/Fedora
 # packaging. Not applicable to Buildroot.