add net451 target to more projects (#2651)

* add net451 target to more projects

* add missing framework assemblies

src/Microsoft.DotNet.Compiler.Common/project.json

@@ -10,6 +10,22 @@
     "Microsoft.DotNet.Files": "1.0.0-*"
   },
   "frameworks": {
+    "net451": {
+      "frameworkAssemblies": {
+        "System.Runtime": {
+          "type": "build"
+        },
+        "System.Collections": {
+          "type": "build"
+        },
+        "System.IO": {
+            "type": "build"
+        },
+        "System.Threading.Tasks": {
+            "type": "build"
+        }
+      }
+    },
     "netstandard1.5": {
       "imports": [
         "portable-net45+wp80+win8+wpa81+dnxcore50"

src/Microsoft.DotNet.Files/project.json

@@ -10,6 +10,19 @@
     "System.Linq.Expressions": "4.0.11-rc2-24022"
   },
   "frameworks": {
+    "net451": {
+      "frameworkAssemblies": {
+        "System.Runtime": {
+          "type": "build"
+        },
+        "System.Collections": {
+          "type": "build"
+        },
+        "System.IO": {
+          "type": "build"
+        }
+      }
+    },
     "netstandard1.5": {
       "imports": [
         "portable-net45+wp80+win8+wpa81+dnxcore50"

src/Microsoft.DotNet.ProjectModel.Workspaces/ProjectJsonWorkspace.cs

@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection.PortableExecutable;
-using System.Runtime.InteropServices;
 using System.Text;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -14,6 +13,7 @@ using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.DotNet.Cli.Compiler.Common;
 using Microsoft.DotNet.ProjectModel.Compilation;
+using Microsoft.Extensions.PlatformAbstractions;
 using NuGet.Frameworks;
 
 namespace Microsoft.DotNet.ProjectModel.Workspaces
@@ -189,10 +189,10 @@ namespace Microsoft.DotNet.ProjectModel.Workspaces
             bool optimize = compilerOptions.Optimize ?? false;
             bool warningsAsErrors = compilerOptions.WarningsAsErrors ?? false;
 
-            Platform platform;
+            Microsoft.CodeAnalysis.Platform platform;
             if (!Enum.TryParse(value: platformValue, ignoreCase: true, result: out platform))
             {
-                platform = Platform.AnyCpu;
+                platform = Microsoft.CodeAnalysis.Platform.AnyCpu;
             }
 
             options = options
@@ -213,7 +213,7 @@ namespace Microsoft.DotNet.ProjectModel.Workspaces
             {
                 keyFile = Path.GetFullPath(Path.Combine(projectDirectory, compilerOptions.KeyFile));
 
-                if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) || useOssSigning)
+                if (PlatformServices.Default.Runtime.OperatingSystemPlatform != Extensions.PlatformAbstractions.Platform.Windows || useOssSigning)
                 {
                     return options.WithCryptoPublicKey(
                         SnkUtils.ExtractPublicKey(File.ReadAllBytes(keyFile)));

src/Microsoft.DotNet.ProjectModel.Workspaces/project.json

@@ -9,6 +9,19 @@
     "Microsoft.CodeAnalysis.CSharp.Workspaces": "1.3.0-beta1-20160410-01 "
   },
   "frameworks": {
+    "net451": {
+      "frameworkAssemblies": {
+        "System.Runtime": {
+          "type": "build"
+        },
+        "System.Collections": {
+          "type": "build"
+        },
+        "System.IO": {
+          "type": "build"
+        }
+      }
+    },
     "netstandard1.5": {
       "imports": [
         "portable-net45+wp80+win8+wpa81+dnxcore50",