Added warning about outdated feature into Kaleidoscope tutorial text
**Motivation: ** I have been studying LLVM with LLVM Kaleidoscope tutorial. In the 4th part I faced an error which said that I can't redefine a function as shown in the tutorial. After hours of searching, I finally found the reason that produced the error is that the feature of symbols redefinition has been disabled since LLVM-9. There was no information about that in the tutorial's text, so I've decided to add a warning.
**Changes**: The only file I fixed is "`llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl04.rst`", I added text warning which says that described feature is outdated and the described functionality will not work properly on LLVM versions older 8 one.
Patch by : DKay7
Differential Revision: https://reviews.llvm.org/D130613
GitOrigin-RevId: fdc950958ed0970159071cc4367a66149971586f
1 file changed
