Solaris needs an included header for alloca

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@39797 91177308-0d34-0410-b5e6-96231b3b80d8

Lex/Preprocessor.cpp

@@ -37,6 +37,7 @@
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/SmallVector.h"
 #include <iostream>
+#include <alloca.h>
 using namespace clang;
 
 //===----------------------------------------------------------------------===//