add a github action job for the main branch to build and upload binaries

Summary:
* add a basic github action job that runs on push to `main`.
  * inspired by the workflow from a reddit thread: https://www.reddit.com/r/rust/comments/12dphrq/comment/jf89urm/
* build a bunch of buck2 and upload as artifacts, they are by default retained for 90 days
* good
  * binaries uploaded and marked with target triple
* could be improved
  * users will have to go to the latest action page to find the artifact. trying to figure out how to best point users to it (there should be a link to the latest job off of main)
  * on macos getting the binary to run was a bit clunky (had to chmod, open and confirm it's safe etc)
* note for myself: I can't tell if the rust cache is working properly so trying to read up on it / monitor

Reviewed By: ndmitchell

Differential Revision: D44791506

fbshipit-source-id: b94d4d22b2ba14938f160a1fc1f04733366ea32a

.github/workflows/upload_buck2.yml

@@ -0,0 +1,77 @@
+name: Build and upload Buck2 binaries
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - os: 'ubuntu-22.04'
+            triple: 'aarch64-unknown-linux-gnu'
+            cross: true
+          - os: 'ubuntu-22.04'
+            triple: 'aarch64-unknown-linux-musl'
+            cross: true
+          - os: 'ubuntu-22.04'
+            triple: 'x86_64-unknown-linux-gnu'
+          # - os: 'ubuntu-22.04'
+          #   triple: 'x86_64-unknown-linux-musl' # Doesn't build
+          - os: 'macos-12'
+            triple: 'aarch64-apple-darwin'
+          - os: 'macos-12'
+            triple: 'x86_64-apple-darwin'
+          - os: 'windows-2022'
+            triple: 'x86_64-pc-windows-msvc'
+    runs-on: ${{ matrix.target.os }}
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - uses: Swatinem/rust-cache@v2
+        with:
+          key: ${{ matrix.target.os }}
+
+      - uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: nightly-2023-01-24
+          targets: ${{ matrix.target.triple }}
+
+      - uses: actions-rs/[email protected]
+        if: matrix.target.cross
+        with:
+          crate: cross
+          version: latest
+
+      - name: Build
+        shell: bash
+        run: |
+          if [ -n "${{ matrix.target.cross }}" ]; then
+            CARGO=cross
+          else
+            CARGO=cargo
+          fi
+
+          $CARGO build --release --bin buck2 --target ${{ matrix.target.triple }}
+          mkdir upload
+          cp target/${{ matrix.target.triple }}/release/buck2* upload/
+
+      - name: Upload (non-Windows)
+        if: runner.os != 'Windows'
+        uses: actions/upload-artifact@v3
+        with:
+          name: buck2-${{ matrix.target.triple }}
+          path: upload/buck2
+
+      - name: Upload (Windows)
+        if: runner.os == 'Windows'
+        uses: actions/upload-artifact@v3
+        with:
+          name: buck2-${{ matrix.target.triple }}
+          path: upload/buck2.exe