swig@3 is keg-only and not linked by default so add linking so that the build scripts can find it

.azure-pipelines/steps/run.yml

@@ -38,6 +38,7 @@ steps:
     brew update
     brew install xz
     brew install swig@3
+    brew link --force swig@3
   displayName: Install build dependencies (OSX)
   condition: and(succeeded(), eq(variables['Agent.OS'], 'Darwin'), eq(variables['SCRIPT'],'./x.py dist'))
 

.travis.yml

@@ -264,6 +264,7 @@ install:
             travis_retry brew update &&
             travis_retry brew install xz &&
             travis_retry brew install swig@3;
+            brew link --force swig@3
           fi &&
           travis_retry curl -fo /usr/local/bin/sccache https://s3-us-west-1.amazonaws.com/rust-lang-ci2/rust-ci-mirror/2018-04-02-sccache-x86_64-apple-darwin &&
             chmod +x /usr/local/bin/sccache &&