Change Linux Platform to support non-host Linux architectures

[ted]

Summary

This was originally http://reviews.llvm.org/D8709 , but I didn't commit it correctly.

Since then GetSupportedArchitectureAtIndex() has been changed. That change, http://reviews.llvm.org/D9511 , breaks non-x86 linux implementations, so this change goes back to the old implementation and adds remote linux support from D8709.

D8709 summary:

The Linux Platform currently will only say the Host architecture is supported. This patch retains that behavior for the Host Platform, but adds a list of architectures for the Remote Platform.

[flackr]

Repeating my comment in what seems to be the active patch. Do we need to enumerate all of the architectures? I put up http://reviews.llvm.org/D9672 earlier today to get non x86 working again where it queries the remote PlatformGdbServer if not the host. WDTY?

[clayborg]

Ideally we should only be enumerating the architectures that are actually built into the llvm/clang that we build, but this is much better than what was being done before.

[ted]

What I'm trying to do is allow a user to load an arbitrary Linux binary and have LLDB select the Remote Linux Platform, if the architecture is one of our supported Linuxes. My goal is to be able to remotely debug Hexagon Linux binaries on Windows.

Currently, this only works if the Host and Remote architectures match. Querying the gdbserver will only work if you're connected, which is not the case when you are doing a target create.

[clayborg]

This is ok. This needs to be merged with the other patch where in the non host else clause it will check if it is connected and if it is connected, it queries the remote platform for the result.

[clayborg]

So the else clause should check if connected to the remote platform, and if it is, check with the connected remote platform, else do what you do in the else clause. We don't require being connected in order to have a platform say that it can handle an architecture.

[ted]

Adding table after check for remote platform, as requested.

[clayborg]

Looks good.

source/Plugins/Platform/Linux/PlatformLinux.cpp

if (IsHost())
                 }
             }
         }
     }
     else
     {
         if (m_remote_platform_sp)
             return m_remote_platform_sp->GetSupportedArchitectureAtIndex(idx, arch);
+
+        llvm::Triple triple;
+        // Set the OS to linux
+        triple.setOS(llvm::Triple::Linux);
+        // Set the architecture
+        switch (idx)
+        {
+            case 0: triple.setArchName("x86_64"); break;
+            case 1: triple.setArchName("i386"); break;
+            case 2: triple.setArchName("arm"); break;
+            case 3: triple.setArchName("aarch64"); break;
+            case 4: triple.setArchName("mips64"); break;
+            case 5: triple.setArchName("hexagon"); break;
+            case 6: triple.setArchName("mips"); break;
+            default: return false;
+        }
+        // Leave the vendor as "llvm::Triple:UnknownVendor" and don't specify the vendor by
+        // calling triple.SetVendorName("unknown") so that it is a "unspecified unknown".
+        // This means when someone calls triple.GetVendorName() it will return an empty string
+        // which indicates that the vendor can be set when two architectures are merged
+
+        // Now set the triple into "arch" and return true
+        arch.SetTriple(triple);
+        return true;
     }
     return false;
 }
 
 void
 PlatformLinux::GetStatus (Stream &strm)
 {
     Platform::GetStatus(strm);