Support for generating ELF objects on Windows.

This adds 'elf' as a recognized target triple environment value and overrides the default generated object format on Windows platforms if that value is present.  This patch also enables MCJIT tests on Windows using the new environment value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165030 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 68464ed..3809f3d 100644
--- a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -453,7 +453,7 @@
   if (TheTriple.isOSDarwin() || TheTriple.getEnvironment() == Triple::MachO)
     return new DarwinX86_32AsmBackend(T, CPU);
 
-  if (TheTriple.isOSWindows())
+  if (TheTriple.isOSWindows() && TheTriple.getEnvironment() != Triple::ELF)
     return new WindowsX86AsmBackend(T, false, CPU);
 
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
@@ -466,7 +466,7 @@
   if (TheTriple.isOSDarwin() || TheTriple.getEnvironment() == Triple::MachO)
     return new DarwinX86_64AsmBackend(T, CPU);
 
-  if (TheTriple.isOSWindows())
+  if (TheTriple.isOSWindows() && TheTriple.getEnvironment() != Triple::ELF)
     return new WindowsX86AsmBackend(T, true, CPU);
 
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
diff --git a/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp b/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
index 02b586b..c48f770 100644
--- a/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
@@ -384,11 +384,15 @@
       MAI = new X86_64MCAsmInfoDarwin(TheTriple);
     else
       MAI = new X86MCAsmInfoDarwin(TheTriple);
+  } else if (TheTriple.getEnvironment() == Triple::ELF) {
+    // Force the use of an ELF container.
+    MAI = new X86ELFMCAsmInfo(TheTriple);
   } else if (TheTriple.getOS() == Triple::Win32) {
     MAI = new X86MCAsmInfoMicrosoft(TheTriple);
   } else if (TheTriple.getOS() == Triple::MinGW32 || TheTriple.getOS() == Triple::Cygwin) {
     MAI = new X86MCAsmInfoGNUCOFF(TheTriple);
   } else {
+    // The default is ELF.
     MAI = new X86ELFMCAsmInfo(TheTriple);
   }
 
@@ -470,7 +474,7 @@
   if (TheTriple.isOSDarwin() || TheTriple.getEnvironment() == Triple::MachO)
     return createMachOStreamer(Ctx, MAB, _OS, _Emitter, RelaxAll);
 
-  if (TheTriple.isOSWindows())
+  if (TheTriple.isOSWindows() && TheTriple.getEnvironment() != Triple::ELF)
     return createWinCOFFStreamer(Ctx, MAB, *_Emitter, _OS, RelaxAll);
 
   return createELFStreamer(Ctx, MAB, _OS, _Emitter, RelaxAll, NoExecStack);
diff --git a/lib/Target/X86/X86Subtarget.h b/lib/Target/X86/X86Subtarget.h
index ed243ec..f723c66 100644
--- a/lib/Target/X86/X86Subtarget.h
+++ b/lib/Target/X86/X86Subtarget.h
@@ -237,10 +237,10 @@
   bool isTargetSolaris() const {
     return TargetTriple.getOS() == Triple::Solaris;
   }
-
-  // ELF is a reasonably sane default and the only other X86 targets we
-  // support are Darwin and Windows. Just use "not those".
-  bool isTargetELF() const { return TargetTriple.isOSBinFormatELF(); }
+  bool isTargetELF() const {
+    return (TargetTriple.getEnvironment() == Triple::ELF ||
+            TargetTriple.isOSBinFormatELF());
+  }
   bool isTargetLinux() const { return TargetTriple.getOS() == Triple::Linux; }
   bool isTargetNaCl() const {
     return TargetTriple.getOS() == Triple::NativeClient;
@@ -251,7 +251,10 @@
   bool isTargetMingw() const { return TargetTriple.getOS() == Triple::MinGW32; }
   bool isTargetCygwin() const { return TargetTriple.getOS() == Triple::Cygwin; }
   bool isTargetCygMing() const { return TargetTriple.isOSCygMing(); }
-  bool isTargetCOFF() const { return TargetTriple.isOSBinFormatCOFF(); }
+  bool isTargetCOFF() const {
+    return (TargetTriple.getEnvironment() != Triple::ELF &&
+            TargetTriple.isOSBinFormatCOFF());
+  }
   bool isTargetEnvMacho() const { return TargetTriple.isEnvironmentMachO(); }
 
   bool isTargetWin64() const {