remove unused variables and defines

Many variables being declared in the Makefiles are Linux specific
and never used by Zephyr.
This is an attempt to cleanup the Makefiles and just keep the code
we use.

Change-Id: Ib97d3d7e3a55077d6f9ec2b4170b3763424a1c99
Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Makefile

@@ -260,11 +260,9 @@ endif
 # Decide whether to build built-in, modular, or both.
 # Normally, just do built-in.
 
-KBUILD_MODULES :=
 KBUILD_BUILTIN := 1
 
-
-export KBUILD_MODULES KBUILD_BUILTIN
+export KBUILD_BUILTIN
 export KBUILD_CHECKSRC KBUILD_SRC
 
 ifneq ($(CC),)
@@ -308,11 +306,6 @@ PYTHON		= python
 CHECK		= sparse
 
 CHECKFLAGS     := -Wbitwise -Wno-return-void $(CF)
-CFLAGS_MODULE   =
-AFLAGS_MODULE   =
-LDFLAGS_MODULE  =
-CFLAGS_KERNEL	=
-AFLAGS_KERNEL	=
 CFLAGS_GCOV	= -fprofile-arcs -ftest-coverage
 
 ifeq ($(COMPILER),clang)
@@ -361,8 +354,6 @@ KBUILD_CFLAGS   := -c -g -std=c99 \
 		-Wno-format-zero-length \
 		-Wno-main -ffreestanding
 
-KBUILD_AFLAGS_KERNEL :=
-KBUILD_CFLAGS_KERNEL :=
 KBUILD_AFLAGS   := -c -g -xassembler-with-cpp
 
 LDFLAGS += $(call ld-option,-nostartfiles)
@@ -377,13 +368,10 @@ export KERNELRELEASE KERNELVERSION
 export ARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP
 export MAKE AWK INSTALLKERNEL PERL PYTHON GENIDT GENOFFSET_H
-export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
+export HOSTCXX HOSTCXXFLAGS CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS ZEPHYRINCLUDE OBJCOPYFLAGS LDFLAGS
-export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV
-export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
-export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
-export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
+export KBUILD_CFLAGS CFLAGS_GCOV KBUILD_AFLAGS AFLAGS_KERNEL
 export KBUILD_ARFLAGS