Update mono props: support OSX and more .NET Framework versions (#6181)

* Update mono props: support OSX and more .NET Framework versions

A potential solve for #6180 that uses msbuild built-ins to determine the target OS and pivots off of that to set the FrameworkPathOverride.  I included a `MonoRoot` property to allow for easy integration into the build process that fsharp/fsharp uses, which allows for a 'floating' mono root.

* add osx build jobs matching the linux jobs, and add a matrix entry to build the compiler for .net framework using mono

* don't try to build anything for .net framework on non-windows

this required additional build work that may conflict with upcoming work, so we'll just settle for building the existing components on macos at all in CI

.vsts-pr.yaml

@@ -4,12 +4,11 @@ jobs:
     vmImage: ubuntu-16.04
   timeoutInMinutes: 90
   strategy:
-    maxParallel: 2
+    maxParallel: 3
     matrix:
       dotnet_sdk:
         _command: make
         _args: Configuration=release
-      # disabled until it can be properly fixed
       release_fcs:
         _command: ./fcs/build.sh
         _args: Build
@@ -23,6 +22,29 @@ jobs:
     continueOnError: true
     condition: failed()
 
+- job: MacOS
+  pool:
+    vmImage: macOS-10.13
+  timeoutInMinutes: 90
+  strategy:
+    maxParallel: 3
+    matrix:
+      dotnet_sdk:
+        _command: make
+        _args: Configuration=release
+      release_fcs:
+        _command: ./fcs/build.sh
+        _args: Build
+  steps:
+  - script: $(_command) $(_args)
+  - task: PublishBuildArtifacts@1
+    inputs:
+      PathtoPublish: '$(Build.SourcesDirectory)/artifacts/TestResults'
+      ArtifactName: 'MacOS $(_command) $(_args)'
+      publishLocation: Container
+    continueOnError: true
+    condition: failed()
+
 - job: Windows
   pool:
     vmImage: vs2017-win2016

FSharpBuild.Directory.Build.props

@@ -44,9 +44,19 @@
 
   <!-- mono -->
   <PropertyGroup Condition="'$(OS)' == 'Unix'">
+    <MonoRoot Condition="'$(MonoRoot)' == '' and $([MSBuild]::IsOsPlatform('Linux'))">/usr</MonoRoot>
+    <MonoRoot Condition="'$(MonoRoot)' == '' and $([MSBuild]::IsOsPlatform('OSX'))">/Library/Frameworks/Mono.framework/Versions/Current</MonoRoot>
+    <MonoLibFolder>$(MonoRoot)/lib/mono</MonoLibFolder>
     <MonoPackaging Condition="$(TargetFramework.StartsWith('net4'))">true</MonoPackaging>
-    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net45'">/usr/lib/mono/4.5-api</FrameworkPathOverride>
-    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net46'">/usr/lib/mono/4.6-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net45'">$(MonoLibFolder)/4.5-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net451'">$(MonoLibFolder)/4.5.1-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net452'">$(MonoLibFolder)/4.5.2-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net46'">$(MonoLibFolder)/4.6-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net461'">$(MonoLibFolder)/4.6.1-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net462'">$(MonoLibFolder)/4.6.2-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net47'">$(MonoLibFolder)/4.7-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net471'">$(MonoLibFolder)/4.7.1-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net472'">$(MonoLibFolder)/4.7.2-api</FrameworkPathOverride>
   </PropertyGroup>
 
   <!-- signing -->