llvm-project

22079e3f - [libc][hdrgen] Add extra_standards and license_text (#165459)

[libc][hdrgen] Add extra_standards and license_text (#165459) This adds a few new features to hdrgen, all meant to facilitate using it with inputs and outputs that are outside the llvm-libc source tree. The new `extra_standards` field is a dictionary to augment the set of names that can be used in `standards` lists. The keys are the identifiers used in YAML ("stdc") and the values are the pretty names generated in the header comments ("Standard C"). This lets a libc project that's leveraging the llvm-libc sources along with its own code define new APIs outside the formal and de facto standards that llvm-libc draws its supported APIs from. The new `license_text` field is a list of lines of license text that replaces the standard LLVM license text used at the top of each generated header. This lets other projects use hdrgen with their own inputs to produce generated headers that are not tied to the LLVM project. Finally, for any function attributes that are not in a canonical list known to be provided by __llvm-libc-common.h, an include will be generated for "llvm-libc-macros/{attribute name}.h", expecting that file to define the "attribute" name as a macro. All this can be used immediately by builds that drive hdrgen and build libc code outside the LLVM CMake build. Future changes could add CMake plumbing to facilitate augmenting the LLVM CMake build of libc with outside sources via overlays and cache files.