Revert layering changes

This reverts:
  r328072 "Move Compiler.h from Support to Demangler to fix layering."
  r328073 "Fix the actual user of DataTypes.h in llvm-c to avoid the circular dependency"

Failing bots:
  http://green.lab.llvm.org/green/job/clang-stage2-coverage-R/
  http://green.lab.llvm.org/green/job/clang-stage2-configure-Rlto/

llvm-svn: 328085
diff --git a/llvm/include/llvm-c/Support.h b/llvm/include/llvm-c/Support.h
index 37d5d72..6de184c 100644
--- a/llvm/include/llvm-c/Support.h
+++ b/llvm/include/llvm-c/Support.h
@@ -14,8 +14,8 @@
 #ifndef LLVM_C_SUPPORT_H
 #define LLVM_C_SUPPORT_H
 
-#include "llvm-c/DataTypes.h"
 #include "llvm-c/Types.h"
+#include "llvm/Support/DataTypes.h"
 
 #ifdef __cplusplus
 extern "C" {