Drop CXX_STD in Makevars (#168)

Author: erikcs

azure-pipelines.yml

@@ -13,6 +13,10 @@ jobs:
         imageName: "ubuntu-latest"
       macos:
         imageName: "macOS-latest"
+        cppVer: "CXX20"
+      macos_cpp11:
+        imageName: "macOS-latest"
+        cppVer: "CXX11"
   pool:
     vmImage: $(imageName)
 
@@ -36,6 +40,11 @@ jobs:
       sudo apt-get install -qq valgrind
     displayName: Setup valgrind
     condition: eq(variables['Agent.OS'], 'Linux')
+  - script: |
+      echo CXX_STD = $(cppVer) >> Makevars
+    workingDirectory: r-package/policytree/src
+    displayName: Specify CXX_STD in R Makevars
+    condition: ne(variables['Agent.OS'], 'Linux')
   - script: |
       curl -OLs https://eddelbuettel.github.io/r-ci/run.sh && chmod 0755 run.sh
       ./run.sh bootstrap