[openwrt/openwrt] build: use -nostdinc and -isystem in NOSTDINC_FLAGS for out-of-tree kernel modules

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/95b838f75bd96705d5192acc56af34801ed6854d

commit 95b838f75bd96705d5192acc56af34801ed6854d
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Mar 18 07:22:11 2021 +0100

    build: use -nostdinc and -isystem in NOSTDINC_FLAGS for out-of-tree kernel modules
    
    This resolves issues uncovered by musl updates
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
    (cherry-picked from commit 9ac47ee46918c45b91f4e4d1fa76b1e26b9d57fe)
---
 include/kernel.mk                    | 3 +++
 package/kernel/ath10k-ct/Makefile    | 3 ++-
 package/kernel/mt76/Makefile         | 3 ++-
 package/kernel/mwlwifi/Makefile      | 3 ++-
 package/kernel/rtl8812au-ct/Makefile | 3 ++-
 5 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/kernel.mk b/include/kernel.mk
index d2a5b42138..e4074a48f4 100644
--- a/include/kernel.mk
+++ b/include/kernel.mk
@@ -118,6 +118,9 @@ KERNEL_MAKE_FLAGS = \
 	cmd_syscalls= \
 	$(if $(__package_mk),KBUILD_EXTRA_SYMBOLS="$(wildcard $(PKG_SYMVERS_DIR)/*.symvers)")
 
+KERNEL_NOSTDINC_FLAGS = \
+	-nostdinc $(if $(DUMP),, -isystem $(shell $(TARGET_CC) -print-file-name=include))
+
 ifeq ($(call qstrip,$(CONFIG_EXTERNAL_KERNEL_TREE))$(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI)),)
   KERNEL_MAKE_FLAGS += \
 	KERNELRELEASE=$(LINUX_VERSION)
diff --git a/package/kernel/ath10k-ct/Makefile b/package/kernel/ath10k-ct/Makefile
index 32b294a69f..a225bd8b19 100644
--- a/package/kernel/ath10k-ct/Makefile
+++ b/package/kernel/ath10k-ct/Makefile
@@ -52,7 +52,8 @@ $(call KernelPackage/ath10k-ct)
   VARIANT:=smallbuffers
 endef
 
-NOSTDINC_FLAGS = \
+NOSTDINC_FLAGS := \
+	$(KERNEL_NOSTDINC_FLAGS) \
 	-I$(PKG_BUILD_DIR) \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport/uapi \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport \
diff --git a/package/kernel/mt76/Makefile b/package/kernel/mt76/Makefile
index 810ee4c3d4..45375ef564 100644
--- a/package/kernel/mt76/Makefile
+++ b/package/kernel/mt76/Makefile
@@ -235,7 +235,8 @@ endef
 
 TARGET_CFLAGS += -I$(STAGING_DIR)/usr/include/libnl-tiny
 
-NOSTDINC_FLAGS = \
+NOSTDINC_FLAGS := \
+	$(KERNEL_NOSTDINC_FLAGS) \
 	-I$(PKG_BUILD_DIR) \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport/uapi \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport \
diff --git a/package/kernel/mwlwifi/Makefile b/package/kernel/mwlwifi/Makefile
index 749fbbe90f..eb986dca03 100644
--- a/package/kernel/mwlwifi/Makefile
+++ b/package/kernel/mwlwifi/Makefile
@@ -34,7 +34,8 @@ define KernelPackage/mwlwifi
   AUTOLOAD:=$(call AutoLoad,50,mwlwifi)
 endef
 
-NOSTDINC_FLAGS = \
+NOSTDINC_FLAGS := \
+	$(KERNEL_NOSTDINC_FLAGS) \
 	-I$(PKG_BUILD_DIR) \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport/uapi \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport \
diff --git a/package/kernel/rtl8812au-ct/Makefile b/package/kernel/rtl8812au-ct/Makefile
index aac754de7f..4dab3fd232 100644
--- a/package/kernel/rtl8812au-ct/Makefile
+++ b/package/kernel/rtl8812au-ct/Makefile
@@ -31,7 +31,8 @@ define KernelPackage/rtl8812au-ct
   PROVIDES:=kmod-rtl8812au
 endef
 
-NOSTDINC_FLAGS = \
+NOSTDINC_FLAGS := \
+	$(KERNEL_NOSTDINC_FLAGS) \
 	-I$(PKG_BUILD_DIR) \
 	-I$(PKG_BUILD_DIR)/include \
 	-I$(STAGING_DIR)/usr/include/mac80211-backport \