build: Redo LLVM macros to disable JIT rather than stop build if headers not found. * configure.ac: Move functionality for OCTAVE_LLVM_IR_DIR, OCTAVE_LLVM_IRBUILDER_HEADER, OCTAVE_LLVM_DATALAYOUT_HEADER macros from acinclude.m4 to configure.ac. * m4/acinclude.m4: Delete OCTAVE_LLVM_IR_DIR, OCTAVE_LLVM_IRBUILDER_HEADER, OCTAVE_LLVM_DATALAYOUT_HEADER macros. Eliminate unnecessary else clause of OCTAVE_LLVM_FUNCTION_ADDATTRIBUTE_API, OCTAVE_LLVM_FUNCTION_ADDFNATTR_API, OTAVE_LLVM_CALLINST_ADDATTRIBUTE_API macros.

FCN_FILE_DIRS += help

help_PRIVATE_FCN_FILES = \
  help/private/__additional_help_message__.m \
  help/private/__strip_html_tags__.m

help_FCN_FILES = \
  help/__makeinfo__.m \
  help/__unimplemented__.m \
  help/doc.m \
  help/doc_cache_create.m \
  help/get_first_help_sentence.m \
  help/help.m \
  help/lookfor.m \
  help/print_usage.m \
  help/type.m \
  help/which.m \
  $(help_PRIVATE_FCN_FILES)

FCN_FILES += $(help_FCN_FILES)

PKG_ADD_FILES += help/PKG_ADD

DIRSTAMP_FILES += help/$(octave_dirstamp)