ci: enable leak checking on osx

(cherry picked from commit b00672b9)

.vsts-ci.yml

@@ -46,6 +46,7 @@ phases:
     displayName: Test
     env:
       TMPDIR: $(Agent.TempDirectory)
+      LEAK_CHECK: leaks
 
 - phase: windows_vs_amd64
   displayName: 'Windows (Visual Studio; amd64)'

ci/setup-macos.sh

@@ -4,3 +4,5 @@ set -x
 
 brew update
 brew install pkgconfig zlib curl openssl libssh2
+
+ln -s /Applications/Xcode.app/Contents/Developer/usr/lib/libLeaksAtExit.dylib /usr/local/lib

script/install-deps-osx.sh

@@ -7,3 +7,5 @@ brew install zlib
 brew install curl
 brew install openssl
 brew install libssh2
+
+ln -s /Applications/Xcode.app/Contents/Developer/usr/lib/libLeaksAtExit.dylib /usr/local/lib