Add gflags

BUG: 67742121
Test: Local build
Change-Id: Iec9fc9fcd9bbe32a50cf28a90eb1d245774013ce

default.xml

@@ -149,6 +149,7 @@
   <project path="external/freetype" name="platform/external/freetype" groups="pdk" />
   <project path="external/fsck_msdos" name="platform/external/fsck_msdos" groups="pdk-cw-fs,pdk-fs" />
   <project path="external/gemmlowp" name="platform/external/gemmlowp" groups="pdk" />
+  <project path="external/gflags" name="platform/external/gflags" groups="pdk" />
   <project path="external/giflib" name="platform/external/giflib" groups="pdk,qcom_msm8x26" />
   <project path="external/glide" name="platform/external/glide" groups="pdk-fs" />
   <project path="external/golang-protobuf" name="platform/external/golang-protobuf" groups="pdk" />