Add external/pcre to default.xml

Bug: 11881977

default.xml

@@ -196,6 +196,7 @@
   <project path="external/openssh" name="platform/external/openssh" />
   <project path="external/openssl" name="platform/external/openssl" groups="pdk" />
   <project path="external/oprofile" name="platform/external/oprofile" />
+  <project path="external/pcre" name="platform/external/pcre" />
   <project path="external/pixman" name="platform/external/pixman" />
   <project path="external/ppp" name="platform/external/ppp" />
   <project path="external/proguard" name="platform/external/proguard" groups="pdk-java" />