Add platform/external/gemmlowp

bug: 22303735

default.xml

@@ -136,6 +136,7 @@
   <project path="external/fonttools" name="platform/external/fonttools" />
   <project path="external/freetype" name="platform/external/freetype" groups="pdk" />
   <project path="external/fsck_msdos" name="platform/external/fsck_msdos" groups="pdk-cw-fs" />
+  <project path="external/gemmlowp" name="platform/external/gemmlowp" />
   <project path="external/giflib" name="platform/external/giflib" groups="pdk-cw-fs,qcom_msm8x26" />
   <project path="external/glide" name="platform/external/glide" />
   <project path="external/gmock" name="platform/external/gmock" groups="pdk" />