[make] add feature to allow multiple parallel build dirs

Using environment variables LKROOT and LKINC you can specify multiple
parallel top level directories (outside of the lk root) that are overlayed
on top of the build system. This allows for a structure like

lk/
testproject/
someotherfirmware/

Where each of these subdirs has an entire overlayed tree of libraries, platforms,
targets, and projects.

To accomplish this, copy makefile into the root dir and build a lk_inc.mk that
sets LKROOT and LKINC.

make/macros.mk

@@ -20,7 +20,7 @@ define MAKECONFIGHEADER
 	echo \#ifndef __$${LDEF}_H > $1.tmp; \
 	echo \#define __$${LDEF}_H >> $1.tmp; \
 	for d in `echo $($2) | tr '[:lower:]' '[:upper:]'`; do \
-		echo "#define $$d" | sed "s/=/\ /g;s/-/_/g;s/\//_/g" >> $1.tmp; \
+		echo "#define $$d" | sed "s/=/\ /g;s/-/_/g;s/\//_/g;s/\./_/g;s/\//_/g" >> $1.tmp; \
 	done; \
 	echo \#endif >> $1.tmp; \
 	if [ -f "$1" ]; then \