[openwrt/openwrt] build: add support for git submodules with CONFIG_SRC_TREE_OVERRIDE

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch master:
https://git.lede-project.org/6fa88be4868836e77b7472dcdde0aeb4f78f8203

commit 6fa88be4868836e77b7472dcdde0aeb4f78f8203
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Wed Apr 25 11:52:20 2018 +0200

    build: add support for git submodules with CONFIG_SRC_TREE_OVERRIDE
    
    Also work around an issue where git would store the modified workdir in
    the submodule git config files
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/package.mk | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/package.mk b/include/package.mk
index 78ea5d0..9912c86 100644
--- a/include/package.mk
+++ b/include/package.mk
@@ -120,7 +120,12 @@ ifdef USE_GIT_TREE
   define Build/Prepare/Default
 	mkdir -p $(PKG_BUILD_DIR)
 	ln -s $(CURDIR)/git-src $(PKG_BUILD_DIR)/.git
-	( cd $(PKG_BUILD_DIR); git checkout .)
+	( cd $(PKG_BUILD_DIR); \
+		git checkout .; \
+		git submodule update --recursive; \
+		git submodule foreach git config --unset core.worktree; \
+		git submodule foreach git checkout .; \
+	)
   endef
 endif
 ifdef USE_SOURCE_DIR