[llvm] [llvm][tblgen] Add `SourcePath` for `emitSourceFileHeader` (PR #65744)

[Shao-Ce SUN via llvm-commits]

sunshaoce wrote:

example for `build/include/llvm/CodeGen/GenVT.inc`
before:
```
/*===- TableGen'erated file -------------------------------------*- C++ -*-===*\
|*                                                                            *|
|* ValueTypes Source Fragment                                                 *|
|*                                                                            *|
|* Automatically generated file, do not edit!                                 *|
|*                                                                            *|
\*===----------------------------------------------------------------------===*/
```
after
```
/*===- TableGen'erated file -------------------------------------*- C++ -*-===*\
|*                                                                            *|
|* ValueTypes Source Fragment                                                 *|
|*                                                                            *|
|* Automatically generated file, do not edit!                                 *|
|* From: llvm/include/llvm/CodeGen/ValueTypes.td                              *|
|*                                                                            *|
\*===----------------------------------------------------------------------===*/
```

https://github.com/llvm/llvm-project/pull/65744