Add external/shflags to the manifest.

Bug: 26113731
TEST=repo sync -j32 -c

Change-Id: Ie5967566a6aa27dc9e1129aded443f1c0e38210e
diff --git a/default.xml b/default.xml
index ea056f2..833bdde 100644
--- a/default.xml
+++ b/default.xml
@@ -109,6 +109,7 @@
   <project path="external/safe-iop" name="platform/external/safe-iop" groups="bdk" />
   <project path="external/selinux" name="platform/external/selinux" groups="bdk" />
   <project path="external/sepolicy" name="platform/external/sepolicy" groups="bdk" />
+  <project path="external/shflags" name="platform/external/shflags" groups="bdk" />
   <project path="external/sonic" name="platform/external/sonic" groups="bdk" />
   <project path="external/sonivox" name="platform/external/sonivox" groups="bdk" />
   <project path="external/speex" name="platform/external/speex" groups="bdk" />