[klibc] Kbuild.install: Copy UAPI headers instead of reinstalling them

Since the UAPI/KAPI header split in Linux 3.7, we have needed
KLIBCKERNELSRC to point to the installed UAPI headers.  Invoking
"make headers_install" in this directory doesn't work.

The previously proposed fix was to invoke make in the parent
directory.  But since we require the headers to be installed
already, we can copy the install tree instead.  Make sure to
dereference any symbolic links while doing this.

Reported-by: Thomas Meyer <thomas@m3y3r.de>
Reported-by: Luis R. Rodriguez <mcgrof@kernel.org>
Link: https://www.zytor.com/pipermail/klibc/2019-January/004033.html
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

scripts/Kbuild.install

diff --git a/scripts/Kbuild.install b/scripts/Kbuild.install
index bafd423..32aec84 100644
--- a/scripts/Kbuild.install
+++ b/scripts/Kbuild.install
@@ -95,7 +95,7 @@
 	$(Q)mkdir -p $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)include
 	$(Q)mkdir -p $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)lib
 	$(Q)mkdir -p $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)bin
-	$(Q)$(MAKE) -C $(KLIBCKERNELSRC) ARCH=$(KLIBCARCH) INSTALL_HDR_PATH=$(INSTALLROOT)$(INSTALLDIR)/$(KCROSS) headers_install
+	$(Q)cp -rfL $(KLIBCKERNELSRC)/include/. $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)include/.
 	$(Q)cp -rf usr/include/. $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)include/.
 	$(Q)chmod -R a+rX,go-w $(INSTALLROOT)$(INSTALLDIR)/$(KCROSS)include
 	$(Q)$(install-data) $(srctree)/klcc/klcc.1 $(INSTALLROOT)$(mandir)/man1/$(KCROSS)klcc.1