Fix CreateFunctionTemplateSpecialization to prevent dangling poiner to stack memory

In ClangASTContext::CreateFunctionTemplateSpecializationInfo a TemplateArgumentList is allocated on the stack but is treated as if it is persistent in subsequent calls. When we exit the function func_decl will still point to the stack allocated memory. We will use TemplateArgumentList::CreateCopy instead which will allocate memory out of the DeclContext.

Differential Revision: https://reviews.llvm.org/D64777

llvm-svn: 366365