gallium/clover: LLVM setLangDefaults moved from clangFrontend to clangBasic
Fixes #6333 (closed) “clover: no member named 'setLangDefaults' in 'clang::CompilerInvocation'”.
Fixes building against LLVM commit 93471e65 and later:
[clang] NFC, move CompilerInvocation::setLangDefaults to LangOptions.h
The function is moved from clangFrontend to clangBasic, which allows tools (e.g. clang pseudoparser) which don't depend on clangFrontend to use.
Differential Revision: https://reviews.llvm.org/D121375
This is my first Mesa commit and Mesa-related merge request, so maybe I missed some how-to.