This code looks as if it is written by Apple, lots of assumptions that
only hold for them and their scenario.

--- tools/clang/lib/Driver/ToolChains.cpp
+++ tools/clang/lib/Driver/ToolChains.cpp
@@ -131,7 +131,7 @@
   GCCVersion[2] = 1;
 
   // Set up the tool chain paths to match gcc.
-  ToolChainDir = "i686-apple-darwin";
+  ToolChainDir = "@GENTOO_PORTAGE_CHOST@";
   ToolChainDir += llvm::utostr(DarwinVersion[0]);
   ToolChainDir += "/";
   ToolChainDir += llvm::utostr(GCCVersion[0]);
@@ -141,9 +141,9 @@
   ToolChainDir += llvm::utostr(GCCVersion[2]);
 
   // Try the next major version if that tool chain dir is invalid.
-  std::string Tmp = "/usr/lib/gcc/" + ToolChainDir;
+  std::string Tmp = "@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir;
   if (!llvm::sys::Path(Tmp).exists()) {
-    std::string Next = "i686-apple-darwin";
+    std::string Next = "@GENTOO_PORTAGE_CHOST_ARCH@";
     Next += llvm::utostr(DarwinVersion[0] + 1);
     Next += "/";
     Next += llvm::utostr(GCCVersion[0]);
@@ -155,7 +155,7 @@
     // Use that if it exists, otherwise hope the user isn't linking.
     //
     // FIXME: Drop dependency on gcc's tool chain.
-    Tmp = "/usr/lib/gcc/" + Next;
+    Tmp = "@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + Next;
     if (llvm::sys::Path(Tmp).exists())
       ToolChainDir = Next;
   }
@@ -168,7 +168,7 @@
     Path += "/x86_64";
     getFilePaths().push_back(Path);
 
-    Path = "/usr/lib/gcc/";
+    Path = "@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/";
     Path += ToolChainDir;
     Path += "/x86_64";
     getFilePaths().push_back(Path);
@@ -179,7 +179,7 @@
   Path += ToolChainDir;
   getFilePaths().push_back(Path);
 
-  Path = "/usr/lib/gcc/";
+  Path = "@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/";
   Path += ToolChainDir;
   getFilePaths().push_back(Path);
 
@@ -188,7 +188,7 @@
   Path += ToolChainDir;
   getProgramPaths().push_back(Path);
 
-  Path = "/usr/libexec/gcc/";
+  Path = "@GENTOO_PORTAGE_EPREFIX@/usr/libexec/gcc/";
   Path += ToolChainDir;
   getProgramPaths().push_back(Path);
 
@@ -291,14 +291,14 @@
 
   // FIXME: Derive these correctly.
   if (getArchName() == "x86_64") {
-    CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir +
+    CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir +
                                          "/x86_64"));
     // Intentionally duplicated for (temporary) gcc bug compatibility.
-    CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir +
+    CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir +
                                          "/x86_64"));
   }
 
-  CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/" + ToolChainDir));
+  CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/" + ToolChainDir));
 
   Tmp = getDriver().Dir + "/../lib/gcc/" + ToolChainDir;
   if (llvm::sys::Path(Tmp).exists())
@@ -306,18 +306,18 @@
   Tmp = getDriver().Dir + "/../lib/gcc";
   if (llvm::sys::Path(Tmp).exists())
     CmdArgs.push_back(Args.MakeArgString("-L" + Tmp));
-  CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir));
+  CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir));
   // Intentionally duplicated for (temporary) gcc bug compatibility.
-  CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir));
+  CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir));
   Tmp = getDriver().Dir + "/../lib/" + ToolChainDir;
   if (llvm::sys::Path(Tmp).exists())
     CmdArgs.push_back(Args.MakeArgString("-L" + Tmp));
   Tmp = getDriver().Dir + "/../lib";
   if (llvm::sys::Path(Tmp).exists())
     CmdArgs.push_back(Args.MakeArgString("-L" + Tmp));
-  CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir +
+  CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir +
                                        "/../../../" + ToolChainDir));
-  CmdArgs.push_back(Args.MakeArgString("-L/usr/lib/gcc/" + ToolChainDir +
+  CmdArgs.push_back(Args.MakeArgString("-L@GENTOO_PORTAGE_EPREFIX@/usr/lib/gcc/" + ToolChainDir +
                                        "/../../.."));
 }
 
@@ -386,22 +386,7 @@
   P.eraseComponent(); // .../usr/bin -> ../usr
   P.appendComponent("lib");
   P.appendComponent("gcc");
-  switch (getTriple().getArch()) {
-  default:
-    assert(0 && "Invalid Darwin arch!");
-  case llvm::Triple::x86:
-  case llvm::Triple::x86_64:
-    P.appendComponent("i686-apple-darwin10");
-    break;
-  case llvm::Triple::arm:
-  case llvm::Triple::thumb:
-    P.appendComponent("arm-apple-darwin10");
-    break;
-  case llvm::Triple::ppc:
-  case llvm::Triple::ppc64:
-    P.appendComponent("powerpc-apple-darwin10");
-    break;
-  }
+  P.appendComponent("@GENTOO_PORTAGE_CHOST@");
   P.appendComponent("4.2.1");
 
   // Determine the arch specific GCC subdirectory.