Add platform/external/slf4j

default.xml

@@ -246,6 +246,7 @@
   <project path="external/sepolicy" name="platform/external/sepolicy" groups="pdk" />
   <project path="external/sfntly" name="platform/external/sfntly" groups="pdk-cw-fs,qcom_msm8x26" />
   <project path="external/skia" name="platform/external/skia" groups="pdk-cw-fs,qcom_msm8x26" />
+  <project path="external/slf4j" name="platform/external/slf4j" />
   <project path="external/smali" name="platform/external/smali" groups="pdk-cw-fs" />
   <project path="external/sonivox" name="platform/external/sonivox" groups="pdk" />
   <project path="external/speex" name="platform/external/speex" groups="pdk" />