kbuild: add option for stripping modules while installing them

Add option for stripping modules while installing them.

This function adds support for stripping modules while they are being
installed.  CONFIG_DEBUG_KERNEL (which will probably become more
popular as developers use kdump) causes the size of the installed
modules to grow by a factor of 9 or so.

Some kernel package systems solve this problem by stripping the debug
information from /lib/modules after running "make modules_install",
but that may not work for people who are installing directly into
/lib/modules --- root partitions that were sized to handle 16 megs
worth of modules may not be quite so happy with 145 megs of modules,
so the "make modules_install" never succeeds.

This patch allows such users to request modules_install to strip the
modules as they are installed.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Documentation/kbuild/makefiles.txt

@@ -1123,6 +1123,14 @@ The top Makefile exports the following variables:
 	$(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE).  The user may
 	override this value on the command line if desired.
 
+    INSTALL_MOD_STRIP
+
+	If this variable is specified, will cause modules to be stripped
+	after they are installed.  If INSTALL_MOD_STRIP is '1', then the
+	default option --strip-debug will be used.  Otherwise,
+	INSTALL_MOD_STRIP will used as the option(s) to the strip command.
+
+
 === 8 Makefile language
 
 The kernel Makefiles are designed to run with GNU Make.  The Makefiles