Make ldconfig configurable

In a cross-compilation set up, running /sbin/ldconfig is useless, so
we make the path to ldconfig configurable through the environment/make
command line. This allows to pass LDCONFIG=/bin/true when doing
cross-compilation.

[Gustavo: update patch for olsr 0.6.4]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

diff -Nura olsrd-0.6.4.orig/make/Makefile.linux olsrd-0.6.4/make/Makefile.linux
--- olsrd-0.6.4.orig/make/Makefile.linux	2013-01-29 09:00:18.041356389 -0300
+++ olsrd-0.6.4/make/Makefile.linux	2013-01-29 09:01:51.598226624 -0300
@@ -3,6 +3,7 @@
 #
 
 ARCH := $(shell uname -m)
+LDCONFIG ?= /sbin/ldconfig
 
 DESTDIR ?=
 prefix ?= /usr/local
@@ -26,9 +27,9 @@
 PLUGIN_SONAME ?= lib$(PLUGIN_NAME).so
 PLUGIN_FULLNAME ?= $(PLUGIN_NAME).so.$(PLUGIN_VER)
 INSTALL_LIB =	install -D -m 755 $(PLUGIN_FULLNAME) $(LIBDIR)/$(PLUGIN_FULLNAME); \
-		/sbin/ldconfig -n $(LIBDIR)
+		$(LDCONFIG) -n $(LIBDIR)
 UNINSTALL_LIB =	rm -f $(LIBDIR)/$(PLUGIN_FULLNAME); \
-		/sbin/ldconfig -n $(LIBDIR)
+		$(LDCONFIG) -n $(LIBDIR)
 
 ifdef OLSRD_PLUGIN
 GENERATE_PIC = true