[libc] delete hdrgen

Thanks to the effort of @RoseZhang03 and @aaryanshukla under the guidance of
@michaelrj-google and @amykhuang, we now have newhdrgen and no longer have a
dependency on TableGen and thus LLVM in order to start bootstrapping a full
build.

This PR:
- Removes being able to set `LIBC_HDRGEN_EXE`.
- LIBC_HDRGEN_EXE; the in tree newhdrgen is the only hdrgen that can be used.
- LIBC_USE_NEW_HEADER_GEN; newhdrgen is the default and only option.
- LIBC_HDRGEN_ONLY; there is no need to have a distinct build step for old
  hdrgen.
- libc-api-test and libc-api-test-tidy build targets.
- Deletes all .td files.

It does not rename newhdrgen to just hdrgen. Will follow up with a distinct PR
for that.

Link: #117209
Fixes: #117208

Author: nickdesaulniers

libc/CMakeLists.txt

@@ -54,27 +54,12 @@ set(LIBC_NAMESPACE ${default_namespace}
 add_subdirectory(newhdrgen)
 
 
-if(LLVM_LIBC_FULL_BUILD OR LLVM_LIBC_GPU_BUILD)
-  if(NOT LIBC_HDRGEN_EXE)
-    # We need to set up hdrgen first since other targets depend on it.
-    add_subdirectory(utils/LibcTableGenUtil)
-    add_subdirectory(utils/HdrGen)
-    # Calling add_tablegen sets variables like LIBC_TABLEGEN_EXE in
-    # PARENT_SCOPE which get lost until saved in the cache.
-    set(LIBC_TABLEGEN_EXE "${LIBC_TABLEGEN_EXE}" CACHE INTERNAL "")
-    set(LIBC_TABLEGEN_TARGET "${LIBC_TABLEGEN_TARGET}" CACHE INTERNAL "")
-  else()
-    message(STATUS "Will use ${LIBC_HDRGEN_EXE} for libc header generation.")
-  endif()
-endif()
 # We will build the GPU utilities if we are not doing a runtimes build.
 option(LIBC_BUILD_GPU_LOADER "Always build the GPU loader utilities" OFF)
 if(LIBC_BUILD_GPU_LOADER OR (LLVM_LIBC_GPU_BUILD AND NOT LLVM_RUNTIMES_BUILD))
   add_subdirectory(utils/gpu)
 endif()
 
-option(LIBC_USE_NEW_HEADER_GEN "Generate header files using new headergen instead of the old one" ON)
-
 set(NEED_LIBC_HDRGEN FALSE)
 if(NOT LLVM_RUNTIMES_BUILD)
   if("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
@@ -88,8 +73,7 @@ if(NOT LLVM_RUNTIMES_BUILD)
     endforeach()
   endif()
 endif()
-option(LIBC_HDRGEN_ONLY "Only build the 'libc-hdrgen' executable" OFF)
-if(LIBC_HDRGEN_ONLY OR NEED_LIBC_HDRGEN)
+if(NEED_LIBC_HDRGEN)
   # When libc is build as part of the runtimes/bootstrap build's CMake run, we
   # only need to build the host tools to build the libc. So, we just do enough
   # to build libc-hdrgen and return.

libc/cmake/modules/LLVMLibCHeaderRules.cmake

@@ -220,46 +220,13 @@ function(add_gen_header target_name)
 
   set(gen_hdr_script "${LIBC_BUILD_SCRIPTS_DIR}/gen_hdr.py")
 
-  file(GLOB td_includes ${LIBC_SOURCE_DIR}/spec/*.td)
-
   set(ENTRYPOINT_NAME_LIST_ARG ${TARGET_ENTRYPOINT_NAME_LIST})
   list(TRANSFORM ENTRYPOINT_NAME_LIST_ARG PREPEND "--e=")
 
-  if(LIBC_HDRGEN_EXE)
-    set(hdrgen_exe ${LIBC_HDRGEN_EXE})
-  else()
-    set(hdrgen_exe ${LIBC_TABLEGEN_EXE})
-    set(hdrgen_deps "${LIBC_TABLEGEN_EXE};${LIBC_TABLEGEN_TARGET}")
-  endif()
-  add_custom_command(
-    OUTPUT ${out_file}
-    COMMAND ${hdrgen_exe} -o ${out_file} --header ${ADD_GEN_HDR_GEN_HDR}
-            --def ${in_file} ${replacement_params} -I ${LIBC_SOURCE_DIR}
-           ${ENTRYPOINT_NAME_LIST_ARG}
-           ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
-
-    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-    DEPENDS ${in_file} ${fq_data_files} ${td_includes}
-            ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
-            ${hdrgen_deps}
-  )
-
   if(LIBC_TARGET_OS_IS_GPU)
     file(MAKE_DIRECTORY ${LIBC_INCLUDE_DIR}/llvm-libc-decls)
     file(MAKE_DIRECTORY ${LIBC_INCLUDE_DIR}/llvm-libc-decls/gpu)
     set(decl_out_file ${LIBC_INCLUDE_DIR}/llvm-libc-decls/${relative_path})
-    add_custom_command(
-      OUTPUT ${decl_out_file}
-      COMMAND ${hdrgen_exe} -o ${decl_out_file}
-              --header ${ADD_GEN_HDR_GEN_HDR} --def ${in_file} --export-decls
-              ${replacement_params} -I ${LIBC_SOURCE_DIR} ${ENTRYPOINT_NAME_LIST_ARG}
-              ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
-
-      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-      DEPENDS ${in_file} ${fq_data_files} ${td_includes}
-              ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
-              ${hdrgen_deps}
-    )
   endif()
 
   if(ADD_GEN_HDR_DEPENDS)