imagemagick: fix magick++-config fixup error

Magic++ bindings are built only with C++ and WCHAR toolchains.
Add a WCHAR toolchain check for the magick++ config fixup.
Looking into the future the fixup shouldn't bail on a missing file so we
can avoid awkward kludges for packages that have many options and config
files.
Fixes:
http://autobuild.buildroot.net/results/33a/33ac4b17866a64379b7bab3c0549f6e075c98dde/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/imagemagick/imagemagick.mk

@@ -19,7 +19,7 @@ IMAGEMAGICK_AUTORECONF = YES
 IMAGEMAGICK_CONFIG_SCRIPTS = \
 	$(addsuffix -config,Magick MagickCore MagickWand Wand)
 
-ifeq ($(BR2_INSTALL_LIBSTDCPP),y)
+ifeq ($(BR2_INSTALL_LIBSTDCPP)$(BR2_USE_WCHAR),yy)
 IMAGEMAGICK_CONFIG_SCRIPTS += Magick++-config
 endif