[openwrt/openwrt] ppp: fix build with kernel 4.14.9+

[LEDE Commits]

mkresin pushed a commit to openwrt/openwrt.git, branch master:
https://git.lede-project.org/04cb1e0fd20196e2e6ec5f8864f5d694f134cbc1

commit 04cb1e0fd20196e2e6ec5f8864f5d694f134cbc1
Author: Mathias Kresin <dev at kresin.me>
AuthorDate: Tue Jan 2 01:01:33 2018 +0100

    ppp: fix build with kernel 4.14.9+
    
    With a9772285a724 ("linux/compiler.h: Split into compiler.h and
    compiler_types.h") compiler.h was refactored and most its content was
    moved to compiler_types.h. Both files are required to build ppp-mod-pppoa.
    
    Signed-off-by: Mathias Kresin <dev at kresin.me>
---
 package/network/services/ppp/Makefile | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/package/network/services/ppp/Makefile b/package/network/services/ppp/Makefile
index 0614ebc..beeaa53 100644
--- a/package/network/services/ppp/Makefile
+++ b/package/network/services/ppp/Makefile
@@ -178,10 +178,15 @@ $(call Build/Configure/Default,, \
 	UNAME_M="$(ARCH)" \
 )
 	mkdir -p $(PKG_BUILD_DIR)/pppd/plugins/pppoatm/linux
-	cp \
+	$(CP) \
 		$(LINUX_DIR)/include/linux/compiler.h \
 		$(LINUX_DIR)/include/$(LINUX_UAPI_DIR)linux/atm*.h \
 		$(PKG_BUILD_DIR)/pppd/plugins/pppoatm/linux/
+
+	# Kernel 4.14.9+ only, ignore the exit status of cp in case the file
+	# doesn't exits
+	-$(CP) $(LINUX_DIR)/include/linux/compiler_types.h \
+		$(PKG_BUILD_DIR)/pppd/plugins/pppoatm/linux/
 endef
 
 TARGET_CFLAGS += -ffunction-sections -fdata-sections