bpo-30688: Support \N{name} escapes in re patterns.

[serhiy-storchaka]

Based on #2261 by @jonathaneunice.

https://bugs.python.org/issue30688

[asottile]

I think this might be causing the clean build to fail:

$ git rev-parse HEAD
a445feb72902e4a3c5ae712f0c289309e1580d52
$ ./configure && make
...
rm -f libpython3.8m.a
ar rcs libpython3.8m.a Modules/getbuildinfo.o Parser/acceler.o Parser/grammar1.o Parser/listnode.o Parser/node.o Parser/parser.o Parser/bitset.o Parser/metagrammar.o Parser/firstsets.o Parser/grammar.o Parser/pgen.o Parser/myreadline.o Parser/parsetok.o Parser/tokenizer.o Objects/abstract.o Objects/accu.o Objects/boolobject.o Objects/bytes_methods.o Objects/bytearrayobject.o Objects/bytesobject.o Objects/call.o Objects/cellobject.o Objects/classobject.o Objects/codeobject.o Objects/complexobject.o Objects/descrobject.o Objects/enumobject.o Objects/exceptions.o Objects/genobject.o Objects/fileobject.o Objects/floatobject.o Objects/frameobject.o Objects/funcobject.o Objects/iterobject.o Objects/listobject.o Objects/longobject.o Objects/dictobject.o Objects/odictobject.o Objects/memoryobject.o Objects/methodobject.o Objects/moduleobject.o Objects/namespaceobject.o Objects/object.o Objects/obmalloc.o Objects/capsule.o Objects/rangeobject.o Objects/setobject.o Objects/sliceobject.o Objects/structseq.o Objects/tupleobject.o Objects/typeobject.o Objects/unicodeobject.o Objects/unicodectype.o Objects/weakrefobject.o Python/_warnings.o Python/Python-ast.o Python/asdl.o Python/ast.o Python/ast_opt.o Python/ast_unparse.o Python/bltinmodule.o Python/ceval.o Python/compile.o Python/codecs.o Python/dynamic_annotations.o Python/errors.o Python/frozenmain.o Python/future.o Python/getargs.o Python/getcompiler.o Python/getcopyright.o Python/getplatform.o Python/getversion.o Python/graminit.o Python/import.o Python/importdl.o Python/marshal.o Python/modsupport.o Python/mysnprintf.o Python/mystrtoul.o Python/pathconfig.o Python/peephole.o Python/pyarena.o Python/pyctype.o Python/pyfpe.o Python/pyhash.o Python/pylifecycle.o Python/pymath.o Python/pystate.o Python/context.o Python/hamt.o Python/pythonrun.o Python/pytime.o Python/bootstrap_hash.o Python/structmember.o Python/symtable.o Python/sysmodule.o Python/thread.o Python/traceback.o Python/getopt.o Python/pystrcmp.o Python/pystrtod.o Python/pystrhex.o Python/dtoa.o Python/formatter_unicode.o Python/fileutils.o Python/dynload_shlib.o    Modules/config.o Modules/getpath.o Modules/main.o Modules/gcmodule.o Modules/posixmodule.o  Modules/errnomodule.o  Modules/pwdmodule.o  Modules/_sre.o  Modules/_codecsmodule.o  Modules/_weakref.o  Modules/_functoolsmodule.o  Modules/_operator.o  Modules/_collectionsmodule.o  Modules/itertoolsmodule.o  Modules/atexitmodule.o  Modules/signalmodule.o  Modules/_stat.o  Modules/timemodule.o  Modules/_threadmodule.o  Modules/_localemodule.o  Modules/_iomodule.o Modules/iobase.o Modules/fileio.o Modules/bytesio.o Modules/bufferedio.o Modules/textio.o Modules/stringio.o  Modules/zipimport.o  Modules/faulthandler.o  Modules/_tracemalloc.o Modules/hashtable.o  Modules/symtablemodule.o  Modules/xxsubtype.o Python/frozen.o
gcc -pthread   -Xlinker -export-dynamic -o python Programs/python.o libpython3.8m.a -lpthread -ldl  -lutil   -lm  
./python -E -S -m sysconfig --generate-posix-vars ;\
if test $? -ne 0 ; then \
	echo "generate-posix-vars failed" ; \
	rm -f ./pybuilddir.txt ; \
	exit 1 ; \
fi
Traceback (most recent call last):
  File "/home/asottile/workspace/cpython/Lib/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/asottile/workspace/cpython/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/asottile/workspace/cpython/Lib/sysconfig.py", line 700, in <module>
    _main()
  File "/home/asottile/workspace/cpython/Lib/sysconfig.py", line 688, in _main
    _generate_posix_vars()
  File "/home/asottile/workspace/cpython/Lib/sysconfig.py", line 350, in _generate_posix_vars
    import pprint
  File "/home/asottile/workspace/cpython/Lib/pprint.py", line 38, in <module>
    import re
  File "/home/asottile/workspace/cpython/Lib/re.py", line 123, in <module>
    import sre_compile
  File "/home/asottile/workspace/cpython/Lib/sre_compile.py", line 14, in <module>
    import sre_parse
  File "/home/asottile/workspace/cpython/Lib/sre_parse.py", line 16, in <module>
    import unicodedata
ModuleNotFoundError: No module named 'unicodedata'
generate-posix-vars failed
Makefile:595: recipe for target 'pybuilddir.txt' failed
make: *** [pybuilddir.txt] Error 1

[asottile]

can confirm, git reset --hard HEAD^ && ./configure && make succeeds

[fangyi-zhou]

Can confirm. Same issue here