move the linux predefined macro definition to the TargetInfo, where it really belongs

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@53149 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 4cf7e7b..ac48e23 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -48,6 +48,11 @@
     Define(Defs, "__APPLE__");
     Define(Defs, "__MACH__");
 #endif
+
+/* FIXME. we may also need to distinguish between darwin and linux targets */
+#ifdef linux
+    Define(Defs, "linux");
+#endif
     
     if (1) {// -fobjc-gc controls this.
       Define(Defs, "__weak", "");