switch to brew install flatc (#447)

Summary:


See context in D49487908, the `flatc` from `brew install flatbuffers` seems good.

Differential Revision: D49530021

Author: cccclai

.ci/docker/common/install_buck.sh

@@ -22,6 +22,11 @@ install_ubuntu() {
   # Cleanup package manager
   apt-get autoclean && apt-get clean
   rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+  sh -c "$(curl -fsSL https://raw.githubusercontent.com/Linuxbrew/install/master/install.sh)"
+  (echo; echo 'eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"') >> /root/.profile
+  eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"
+  mv /home/linuxbrew/.linuxbrew/bin/brew /usr/bin/
 }
 
 # Install base packages depending on the base OS

.ci/docker/conda-env-ci.txt

@@ -1,4 +1 @@
-# TODO: We might need to update this to install flatbuffers from the pinned commit
-# in fbcode/executorch/third-party/flatbuffers.submodule.txt
-flatbuffers=2.0.0
 cmake=3.22.1

.ci/scripts/setup-linux.sh

@@ -20,5 +20,6 @@ fi
 
 # As Linux job is running inside a Docker container, all of its dependencies
 # have already been installed
+install_flatc
 install_executorch
 build_executorch_runner "${BUILD_TOOL}"

.ci/scripts/setup-macos.sh

@@ -27,6 +27,10 @@ install_buck() {
     brew install wget
   fi
 
+  if ! command -v flatc &> /dev/null; then
+    brew install flatbuffers
+  fi
+
   BUCK2_NOT_AVAILABLE=false
   if ! command -v buck2 &> /dev/null; then
     BUCK2_NOT_AVAILABLE=true

.ci/scripts/utils.sh

@@ -15,6 +15,10 @@ retry () {
     "$@" || (sleep 30 && reset_buck && "$@") || (sleep 60 && reset_buck && "$@")
 }
 
+install_flatc() {
+  brew install flatbuffers
+}
+
 install_executorch() {
   which pip
   # Install executorch, this assumes that Executorch is checked out in the

docs/website/docs/tutorials/00_setting_up_executorch.md

@@ -17,7 +17,7 @@ conda create -yn executorch python=3.10.0
 conda activate executorch
 
 conda install cmake
-conda install -c conda-forge flatbuffers
+brew install flatbuffers
 ```
 
 ### Step 2: Clone the `executorch` repo