linux: use host pkg-config when host libelf is set

A patch was added to the Linux kernel in 5.1.0-rc3 which adds a
requirement that the host build environment include pkg-config. Add the
correct host-pkgconf dependency and environment variables to ensure
Linux picks up the correct libraries.

Move the existing LINUX_MAKE_ENV assignment earlier, to simplify the
append-assignment in the libelf conditional block.

Fixes: #11761

Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Suggested-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Stuart Summers <stuart.summers@intel.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Arnout: extend commit message as suggested by Yann]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

(cherry picked from commit 615e2edc2ae8351519448d1965f0c4eec4e793b1)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -59,6 +59,10 @@ BR_NO_CHECK_HASH_FOR += $(notdir $(LINUX_PATCHES))
 # be directories in the patch list (unlike for other packages).
 LINUX_PATCH = $(filter ftp://% http://% https://%,$(LINUX_PATCHES))
 
+LINUX_MAKE_ENV = \
+	$(TARGET_MAKE_ENV) \
+	BR_BINARIES_DIR=$(BINARIES_DIR)
+
 LINUX_INSTALL_IMAGES = YES
 LINUX_DEPENDENCIES = host-kmod
 
@@ -95,7 +99,13 @@ LINUX_DEPENDENCIES += host-openssl
 endif
 
 ifeq ($(BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF),y)
-LINUX_DEPENDENCIES += host-elfutils
+LINUX_DEPENDENCIES += host-elfutils host-pkgconf
+LINUX_MAKE_ENV += \
+	PKG_CONFIG="$(PKG_CONFIG_HOST_BINARY)" \
+	PKG_CONFIG_SYSROOT_DIR="/" \
+	PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 \
+	PKG_CONFIG_ALLOW_SYSTEM_LIBS=1 \
+	PKG_CONFIG_LIBDIR="$(HOST_DIR)/lib/pkgconfig:$(HOST_DIR)/share/pkgconfig"
 endif
 
 # If host-uboot-tools is selected by the user, assume it is needed to
@@ -119,10 +129,6 @@ LINUX_MAKE_FLAGS = \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
 	DEPMOD=$(HOST_DIR)/sbin/depmod
 
-LINUX_MAKE_ENV = \
-	$(TARGET_MAKE_ENV) \
-	BR_BINARIES_DIR=$(BINARIES_DIR)
-
 ifeq ($(BR2_REPRODUCIBLE),y)
 LINUX_MAKE_ENV += \
 	KBUILD_BUILD_VERSION=1 \

package/pkg-kconfig.mk

@@ -179,7 +179,9 @@ endif
 # nconfig, gconfig, xconfig).
 # So we simply remove our PATH and PKG_CONFIG_* variables.
 $(2)_CONFIGURATOR_MAKE_ENV = \
-	$$(filter-out PATH=% PKG_CONFIG=% PKG_CONFIG_SYSROOT_DIR=% PKG_CONFIG_LIBDIR=%,$$($(2)_MAKE_ENV)) \
+	$$(filter-out PATH=% PKG_CONFIG=% PKG_CONFIG_SYSROOT_DIR=% \
+	   PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=% PKG_CONFIG_ALLOW_SYSTEM_LIBS=% \
+	   PKG_CONFIG_LIBDIR=%,$$($(2)_MAKE_ENV)) \
 	PKG_CONFIG_PATH="$(HOST_PKG_CONFIG_PATH)"
 
 # Configuration editors (menuconfig, ...)