dist/azure-build-and-test-vcpkg.yml: fix up macOS vcpkg build (hopefully)

Cf: microsoft/vcpkg#22933 , the guidance seems
to be that automake and libtool need to be installed underneath vcpkg.

Author: pkgw

dist/azure-build-and-test-vcpkg.yml

@@ -22,7 +22,7 @@ steps:
 
 - bash: |
     set -xeuo pipefail
-    brew install pkg-config
+    brew install automake libtool pkg-config
   displayName: "Install vcpkg dependencies (macOS)"
   condition: and(succeeded(), eq(variables['Agent.OS'], 'Darwin'))