package/elfutils: fix build without c++

The version bump to 0.189 with commit
258c27f6335aa66ce634c93b82ab146bf65f7f2 introduced an error when
libstdc++ support is not available and --disable-demangler was not used:
https://sourceware.org/git/?p=elfutils.git;a=commitdiff;h=73e212b0a778c6dbe84f79b7eb2647dea50ea16f

Fixes:
http://autobuild.buildroot.net/results/cd4/cd4ca1a2b2eabe6937cb920cda5d8e566216546e/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/elfutils/elfutils.mk

@@ -66,6 +66,12 @@ ELFUTILS_DEPENDENCIES += argp-standalone
 ELFUTILS_CONF_OPTS += --disable-symbol-versioning
 endif
 
+ifeq ($(BR2_INSTALL_LIBSTDCPP),y)
+ELFUTILS_CONF_OPTS += --enable-demangler
+else
+ELFUTILS_CONF_OPTS += --disable-demangler
+endif
+
 ifeq ($(BR2_PACKAGE_BZIP2),y)
 ELFUTILS_DEPENDENCIES += bzip2
 ELFUTILS_CONF_OPTS += --with-bzlib