Top-level makefile fix for OS agnosticism and set the value of TARGET_ARCH

using grep because the '.config' will not get included if we are doing
a 'clean' or other targets. This was preventing the proper cleaning up
target architecture include files.

Makefile

@@ -26,7 +26,7 @@ noconfig_targets := menuconfig config oldconfig randconfig \
 	defconfig allyesconfig allnoconfig clean distclean \
 	release tags TAGS
 TOPDIR=./
-include Rules.mak
+-include Rules.mak
 
 DIRS = ldso libc libcrypt libresolv libnsl libutil libm libpthread librt
 ifeq ($(strip $(UCLIBC_HAS_GETTEXT_AWARENESS)),y)

Rules.mak

@@ -93,7 +93,7 @@ check_gcc=$(shell if $(CC) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1;
 	then echo "$(1)"; else echo "$(2)"; fi)
 
 # Make certain these contain a final "/", but no "//"s.
-TARGET_ARCH:=$(strip $(subst ",, $(strip $(TARGET_ARCH))))
+TARGET_ARCH:=$(shell grep -s ^TARGET_ARCH .config | sed -e 's/^TARGET_ARCH=//' -e 's/"//g')
 RUNTIME_PREFIX:=$(strip $(subst //,/, $(subst ,/, $(subst ",, $(strip $(RUNTIME_PREFIX))))))
 DEVEL_PREFIX:=$(strip $(subst //,/, $(subst ,/, $(subst ",, $(strip $(DEVEL_PREFIX))))))
 export RUNTIME_PREFIX DEVEL_PREFIX