package/yaml-cpp: fix library name

In the current state this package install libyaml-cppd.so due to "d"
being added because the variable CMAKE_DEBUG_POSTFIX is not set:
https://github.com/jbeder/yaml-cpp/blob/master/CMakeLists.txt#L137

This breaks the build of mongodb which expects the library name
libyaml-cpp.so:
https://github.com/mongodb/mongo/blob/master/SConstruct#L5090

Fixes:
http://autobuild.buildroot.net/results/304/3044d040dec090a2f528a96f201d4e554f6779b4/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 9613092610729177f060bea62708fe3d81c0536b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/yaml-cpp/yaml-cpp.mk

@@ -13,6 +13,7 @@ YAML_CPP_CPE_ID_VENDOR = yaml-cpp_project
 
 # Disable testing and parse tools
 YAML_CPP_CONF_OPTS += \
+	-DCMAKE_DEBUG_POSTFIX="" \
 	-DYAML_CPP_BUILD_TESTS=OFF \
 	-DYAML_CPP_BUILD_TOOLS=OFF