[openwrt/openwrt] uml: headers are not exportable

[LEDE Commits]

chunkeey pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/1ce2691bf3dacca41559a20e7f1a55587469dfae

commit 1ce2691bf3dacca41559a20e7f1a55587469dfae
Author: Christian Lamparter <chunkeey at gmail.com>
AuthorDate: Sat Sep 24 19:57:26 2022 +0200

    uml: headers are not exportable
    
    When building UML this showed up as of late (2022-09-01):
    | Makefile:1335: *** Headers not exportable for UML.  Stop.
    
    This message popped up because of an upstream patch that
    fixed this error not showing up sooner. For more information see:
    <https://lore.kernel.org/lkml/20220901011252.550830-1-masahiroy@kernel.org/T/>
    
    Now, I don't think we can just skip the kernel headers.
    Some userspace applications are going to need these. So,
    The next best alternative I can think of, is to go with
    the headers by the host arch the UML is compiled for.
    (Technically, ARCH= should be safe for all other targets
    as well... But let's not poke a hornet's nest)
    
    Signed-off-by: Christian Lamparter <chunkeey at gmail.com>
---
 include/kernel-defaults.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index 2e21392016..dcba319a0f 100644
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -117,7 +117,7 @@ define Kernel/Configure/Default
 		cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config; \
 		cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev; \
 	}
-	$(_SINGLE) [ -d $(LINUX_DIR)/user_headers ] || $(KERNEL_MAKE) INSTALL_HDR_PATH=$(LINUX_DIR)/user_headers headers_install
+	$(_SINGLE) [ -d $(LINUX_DIR)/user_headers ] || $(KERNEL_MAKE) $(if $(findstring uml,$(BOARD)),ARCH=$(ARCH)) INSTALL_HDR_PATH=$(LINUX_DIR)/user_headers headers_install
 	grep '=[ym]' $(LINUX_DIR)/.config.set | LC_ALL=C sort | $(MKHASH) md5 > $(LINUX_DIR)/.vermagic
 endef