package/igh-ethercat: fix build without C++

tools needs C++ since the addition of the package in commit
27ad470d7df5509ae4a96edd04521211900090e4 resulting in the following
build failure:

no -DHAVE_CONFIG_H -I. -I..   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -I../include -I../master -Wall -DREV=`if test -s ../revision; then cat ../revision; else hg id -i .. 2>/dev/null || echo "unknown"; fi` -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Ofast -g0  -c -o ethercat-Command.o `test -f 'Command.cpp' || echo './'`Command.cpp
/bin/bash: line 1: no: command not found

Fixes:
 - http://autobuild.buildroot.org/results/89d096006839f32a3d03786e69e51ec3c5ea70f6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr: move it before package's options]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 014ebc394d116e886796dd9af377299915cb556d)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/igh-ethercat/igh-ethercat.mk

@@ -15,6 +15,7 @@ IGH_ETHERCAT_INSTALL_STAGING = YES
 IGH_ETHERCAT_CONF_OPTS = \
 	--with-linux-dir=$(LINUX_DIR)
 
+IGH_ETHERCAT_CONF_OPTS += $(if $(BR2_INSTALL_LIBSTDCPP),--enable-tool,--disable-tool)
 IGH_ETHERCAT_CONF_OPTS += $(if $(BR2_PACKAGE_IGH_ETHERCAT_8139TOO),--enable-8139too,--disable-8139too)
 IGH_ETHERCAT_CONF_OPTS += $(if $(BR2_PACKAGE_IGH_ETHERCAT_E100),--enable-e100,--disable-e100)
 IGH_ETHERCAT_CONF_OPTS += $(if $(BR2_PACKAGE_IGH_ETHERCAT_E1000),--enable-e1000,--disable-e1000)