Add MacOS vcpkg triplet

Author: Beanavil

.github/workflows/presubmit.yml

@@ -706,7 +706,7 @@ jobs:
       run: |
         git clone https://github.com/Microsoft/vcpkg.git vcpkg
         ./vcpkg/bootstrap-vcpkg.sh
-        ./vcpkg/vcpkg install tclap glm glew sfml stb
+        ./vcpkg/vcpkg --triplet=x64-osx install tclap glm glew sfml stb
 
     - name: Set up compiler flags
       run: |