build: remove use of STAGING_DIR_HOST/usr (fixes cmake build error on macOS)

This directory is never created, nor is it used anywhere. Using it in
HOST_LDFLAGS causes a linker warning to be emitted on macOS, which
messes with cmake configure tests.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

rules.mk

@@ -244,9 +244,9 @@ export PKG_CONFIG
 
 HOSTCC:=gcc
 HOSTCXX:=g++
-HOST_CPPFLAGS:=-I$(STAGING_DIR_HOST)/include -I$(STAGING_DIR_HOST)/usr/include $(if $(IS_PACKAGE_BUILD),-I$(STAGING_DIR_HOSTPKG)/include -I$(STAGING_DIR)/host/include)
+HOST_CPPFLAGS:=-I$(STAGING_DIR_HOST)/include $(if $(IS_PACKAGE_BUILD),-I$(STAGING_DIR_HOSTPKG)/include -I$(STAGING_DIR)/host/include)
 HOST_CFLAGS:=-O2 $(HOST_CPPFLAGS)
-HOST_LDFLAGS:=-L$(STAGING_DIR_HOST)/lib -L$(STAGING_DIR_HOST)/usr/lib $(if $(IS_PACKAGE_BUILD),-L$(STAGING_DIR_HOSTPKG)/lib -L$(STAGING_DIR)/host/lib)
+HOST_LDFLAGS:=-L$(STAGING_DIR_HOST)/lib $(if $(IS_PACKAGE_BUILD),-L$(STAGING_DIR_HOSTPKG)/lib -L$(STAGING_DIR)/host/lib)
 
 ifeq ($(CONFIG_EXTERNAL_TOOLCHAIN),)
   TARGET_AR:=$(TARGET_CROSS)gcc-ar