fix(driver/bpf): honor CLANG and LLC from the env

the configure subsystem currently relies on
clang and llc being available.
However, building drivers in a containerized
environment might actually want to leverage
a specific CLANG version.
So just like we did for CC on the kmod driver,
have those variables passed over to the
configure subsystem.

Signed-off-by: Gerlando Falauto <gerlando.falauto@sysdig.com>

driver/bpf/configure/Makefile.inc.in

@@ -1,7 +1,7 @@
 MODULE_MAKEFILE_DIR := $(shell dirname $(abspath $(lastword $(MAKEFILE_LIST))))
 
 # Run the module build.sh (wrapper for make) script with an empty environment, but PATH
-HAS_@CONFIGURE_MODULE@ := $(shell env -i PATH="$(PATH)" KERNELDIR="$(KERNELDIR)" sh $(MODULE_MAKEFILE_DIR)/build.sh ; echo $$?)
+HAS_@CONFIGURE_MODULE@ := $(shell env -i CLANG="$(CLANG)" LLC="$(LLC)" PATH="$(PATH)" KERNELDIR="$(KERNELDIR)" sh $(MODULE_MAKEFILE_DIR)/build.sh ; echo $$?)
 
 ifeq ($(HAS_@CONFIGURE_MODULE@),0)
 $(info [configure-bpf] Setting HAS_@CONFIGURE_MODULE@ flag)