alloca.h is needed on Solaris

llvm-svn: 42088
diff --git a/clang/Sema/SemaDecl.cpp b/clang/Sema/SemaDecl.cpp
index b9ac2b7..3985d51 100644
--- a/clang/Sema/SemaDecl.cpp
+++ b/clang/Sema/SemaDecl.cpp
@@ -23,6 +23,7 @@
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/SmallSet.h"
+#include <alloca.h>
 using namespace clang;
 
 Sema::DeclTy *Sema::isTypeName(const IdentifierInfo &II, Scope *S) const {