Add 'install-headers' target in the top-level Makefile

This target recursively locates directories with sdk headers and
installs them all. Useful when you want to build a complete new X
server and drivers without having to install the X server before the
drivers are actually working.

Signed-off-by: Keith Packard <keithp@keithp.com>

Makefile.am

@@ -95,3 +95,10 @@ DIST_SUBDIRS = \
 # gross hack
 relink: all
 	$(AM_V_at)$(MAKE) -C hw relink
+
+install-headers: Makefile
+	+find . -name Makefile | while read m; do			\
+		if grep -q install-sdkHEADERS $$m; then			\
+			(cd `dirname "$$m"` && make install-sdkHEADERS)	\
+		fi							\
+	done