Add MachO S_MOD_INIT_FUNC_POINTERS section type support

Global data initialization is provided by special section types in the
MachO format whose contents are a list of function pointers to
initialize. Add ObjWriter support for these sections through the
existing CustomSectionAttributes enum.

Documentation/Getting-Started-For-Linux-and-OS-X.md

@@ -63,6 +63,8 @@ and building both can be found below.
     $ cmake -DWITH_CORECLR=../../coreclr/path/to/CoreCLR/binaries -DLLVM_OPTIMIZED_TABLEGEN=ON ..
     ```
 
+    Ie, ../../coreclr/bin/Product/OSX.x64.Debug
+
 5. Build LLVM and LLILC:
 
     ```

lib/ObjWriter/.nuget/Microsoft.DotNet.ObjectWriter.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>Microsoft.DotNet.ObjectWriter</id>
-    <version>1.0.10-prerelease-00001</version>
+    <version>1.0.11-prerelease-00001</version>
     <title>Microsoft .NET Object File Generator</title>
     <authors>Microsoft</authors>
     <owners>Microsoft</owners>

lib/ObjWriter/.nuget/runtime.json

@@ -2,17 +2,17 @@
   "runtimes": {
     "win7-x64": {
       "Microsoft.DotNet.ObjectWriter": {
-        "toolchain.win7-x64.Microsoft.DotNet.ObjectWriter": "1.0.10-prerelease-00001"
+        "toolchain.win7-x64.Microsoft.DotNet.ObjectWriter": "1.0.11-prerelease-00001"
       }
     },
     "ubuntu.14.04-x64": {
       "Microsoft.DotNet.ObjectWriter": {
-        "toolchain.ubuntu.14.04-x64.Microsoft.DotNet.ObjectWriter": "1.0.10-prerelease-00001"
+        "toolchain.ubuntu.14.04-x64.Microsoft.DotNet.ObjectWriter": "1.0.11-prerelease-00001"
       }
     },
     "osx.10.10-x64": {
       "Microsoft.DotNet.ObjectWriter": {
-        "toolchain.osx.10.10-x64.Microsoft.DotNet.ObjectWriter": "1.0.10-prerelease-00001"
+        "toolchain.osx.10.10-x64.Microsoft.DotNet.ObjectWriter": "1.0.11-prerelease-00001"
       }
     }
   }

lib/ObjWriter/.nuget/toolchain.osx.10.10-x64.Microsoft.DotNet.ObjectWriter.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>toolchain.osx.10.10-x64.Microsoft.DotNet.ObjectWriter</id>
-    <version>1.0.10-prerelease-00001</version>
+    <version>1.0.11-prerelease-00001</version>
     <title>Microsoft .NET Object File Generator</title>
     <authors>Microsoft</authors>
     <owners>Microsoft</owners>

lib/ObjWriter/.nuget/toolchain.ubuntu.14.04-x64.Microsoft.DotNet.ObjectWriter.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>toolchain.ubuntu.14.04-x64.Microsoft.DotNet.ObjectWriter</id>
-    <version>1.0.10-prerelease-00001</version>
+    <version>1.0.11-prerelease-00001</version>
     <title>Microsoft .NET Object File Generator</title>
     <authors>Microsoft</authors>
     <owners>Microsoft</owners>

lib/ObjWriter/.nuget/toolchain.win7-x64.Microsoft.DotNet.ObjectWriter.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>toolchain.win7-x64.Microsoft.DotNet.ObjectWriter</id>
-    <version>1.0.10-prerelease-00001</version>
+    <version>1.0.11-prerelease-00001</version>
     <title>Microsoft .NET Object File Generator</title>
     <authors>Microsoft</authors>
     <owners>Microsoft</owners>

lib/ObjWriter/objwriter.cpp

@@ -256,6 +256,7 @@ enum CustomSectionAttributes : int32_t {
   CustomSectionAttributes_ReadOnly = 0x0000,
   CustomSectionAttributes_Writeable = 0x0001,
   CustomSectionAttributes_Executable = 0x0002,
+  CustomSectionAttributes_MachO_Init_Func_Pointers = 0x0100,
 };
 
 extern "C" bool CreateCustomSection(ObjectWriter *OW, const char *SectionName,
@@ -281,11 +282,16 @@ extern "C" bool CreateCustomSection(ObjectWriter *OW, const char *SectionName,
                                : SectionKind::getReadOnly();
 
   switch (TheTriple.getObjectFormat()) {
-  case Triple::MachO:
+  case Triple::MachO: {
+    unsigned typeAndAttributes = 0;
+    if (attributes & CustomSectionAttributes_MachO_Init_Func_Pointers) {
+      typeAndAttributes |= MachO::SectionType::S_MOD_INIT_FUNC_POINTERS;
+    }
     Section = OutContext.getMachOSection(
         (attributes & CustomSectionAttributes_Executable) ? "__TEXT" : "__DATA",
-        SectionName, 0, Kind);
+        SectionName, typeAndAttributes, Kind);
     break;
+  }
   case Triple::COFF: {
     unsigned Characteristics = COFF::IMAGE_SCN_MEM_READ;