Move gflags to third-party (#11448)

### Summary

gflags is just used by the runner, so we could technically add it only
if `EXECUTORCH_BUILD_EXECUTOR_RUNNER` is not. However, all the examples
assume gflags is always built and directly uses the library. So for
simplicity, let's just always include it for now (the default right now
anyways).

### Test plan

CI

cc @larryliu0820

Author: jathu

CMakeLists.txt

@@ -430,14 +430,6 @@ endif()
 
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/configurations)
 
-#
-# gflags: Commandline flag host library.
-#
-
-if(EXECUTORCH_BUILD_GFLAGS)
-  add_subdirectory(third-party/gflags)
-endif()
-
 # Install `executorch` library as well as `executorch-config.cmake` under
 # ${CMAKE_INSTALL_PREFIX}/
 install(

backends/apple/coreml/scripts/build_tests.sh

@@ -33,8 +33,7 @@ cmake "$EXECUTORCH_ROOT_PATH" -B"$CMAKE_EXECUTORCH_BUILD_DIR_PATH" \
 -DPLATFORM=MAC_UNIVERSAL \
 -DDEPLOYMENT_TARGET=13.0 \
 -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=OFF \
--DEXECUTORCH_BUILD_XNNPACK=OFF \
--DEXECUTORCH_BUILD_GFLAGS=OFF
+-DEXECUTORCH_BUILD_XNNPACK=OFF
 
 cmake --build "$CMAKE_EXECUTORCH_BUILD_DIR_PATH"  -j9 -t executorch
 

backends/cadence/build_cadence_fusionG3.sh

@@ -50,7 +50,6 @@ if $STEPWISE_BUILD; then
         -DEXECUTORCH_BUILD_KERNELS_CUSTOM=OFF \
         -DPYTHON_EXECUTABLE=python3 \
         -DEXECUTORCH_FUSION_G3_OPT=ON \
-        -DEXECUTORCH_BUILD_GFLAGS=ON \
         -DHAVE_FNMATCH_H=OFF \
         -Bcmake-out/backends/cadence \
         backends/cadence

backends/cadence/build_cadence_hifi4.sh

@@ -49,7 +49,6 @@ if $STEPWISE_BUILD; then
         -DEXECUTORCH_BUILD_KERNELS_CUSTOM=OFF \
         -DPYTHON_EXECUTABLE=python3 \
         -DEXECUTORCH_NNLIB_OPT=ON \
-        -DEXECUTORCH_BUILD_GFLAGS=ON \
         -DHAVE_FNMATCH_H=OFF \
         -Bcmake-out/backends/cadence \
         backends/cadence

third-party/CMakeLists.txt

@@ -5,6 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 add_subdirectory(json)
+add_subdirectory(gflags)
 
 if(EXECUTORCH_BUILD_PYBIND)
   add_subdirectory(pybind11)

tools/cmake/preset/default.cmake

@@ -209,11 +209,6 @@ define_overridable_option(
   "Build the Cortex-M backend"
   BOOL OFF
 )
-define_overridable_option(
-  EXECUTORCH_BUILD_GFLAGS
-  "Build the gflags library."
-  BOOL ON
-)
 define_overridable_option(
   EXECUTORCH_COREML_BUILD_EXECUTOR_RUNNER
   "Build CoreML executor runner."