Add external/ltrace to default.xml

Change-Id: Iea26eb8c84ecacf5e494af0da1ac3c6a84b89a8e

default.xml

@@ -174,6 +174,7 @@
   <project path="external/linux-tools-perf" name="platform/external/linux-tools-perf" />
   <project path="external/littlemock" name="platform/external/littlemock" />
   <project path="external/llvm" name="platform/external/llvm" groups="pdk" />
+  <project path="external/ltrace" name="platform/external/ltrace" />
   <project path="external/lzma" name="platform/external/lzma" />
   <project path="external/marisa-trie" name="platform/external/marisa-trie" />
   <project path="external/markdown" name="platform/external/markdown" />