Steps to reproduce:

$ wget https://www.python.org/ftp/python/3.9.0/Python-3.9.0a4.tar.xz
$ tar xvf Python-3.9.0a4.tar.xz
$ cd Python-3.9.0a4
$ ./configure --with-dtrace
$ make -j12
/usr/bin/ld: libpython3.9.a(ceval.o): in function `_PyEval_EvalFrameDefault':
/home/mplch/Work/fedpkg/Python-3.9.0a4/Python/ceval.c:1117: undefined reference to `python_function__entry_semaphore'
/usr/bin/ld: /home/mplch/Work/fedpkg/Python-3.9.0a4/Python/ceval.c:1254: undefined reference to `python_line_semaphore'
/usr/bin/ld: /home/mplch/Work/fedpkg/Python-3.9.0a4/Python/ceval.c:3697: undefined reference to `python_function__return_semaphore'
/usr/bin/ld: /home/mplch/Work/fedpkg/Python-3.9.0a4/Python/ceval.c:1445: undefined reference to `python_line_semaphore'

...

/usr/bin/ld: libpython3.9.a(gcmodule.o):(.note.stapsdt+0x70): undefined reference to `python_gc__done_semaphore'
collect2: error: ld returned 1 exit status
make: *** [Makefile:709: Programs/_testembed] Error 1


Additional info:
$ gcc --version
gcc (GCC) 9.2.1 20190827 (Red Hat 9.2.1-1)
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I can reproduce this from git and will try to bisect the introducer.

aabdeb766b7fa581e7de01f3c953b12792f0736d is the first new commit
commit aabdeb766b7fa581e7de01f3c953b12792f0736d
Author: David Carlier <dcarlier@afilias.info>
Date:   Tue Jan 28 12:53:32 2020 +0000

    bpo-38960: DTrace build fix for FreeBSD. (GH-17451)
    
    DTrace build fix for FreeBSD.
    
    - allowing passing an extra flag as it need to define the arch size.
    - casting some probe's arguments.

 .../next/Core and Builtins/2019-12-03-16-41-22.bpo-38960.kvoFM0.rst | 1 +
 Python/ceval.c                                                      | 6 +++---
 Python/import.c                                                     | 4 ++--
 Python/sysmodule.c                                                  | 2 +-
 configure                                                           | 3 +--
 configure.ac                                                        | 3 +--
 6 files changed, 9 insertions(+), 10 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2019-12-03-16-41-22.bpo-38960.kvoFM0.rst

Sorry for the inconveniences. I can reproduce on FreeBSD too if I do not set the DFLAGS env var (because FreeBSD needs architecture bits in addition). What happens when make distclean && export DFLAGS="" && ./configure --with-dtrace ?

export DFLAGS="" does not seem to workaround this.

$ make distclean && export DFLAGS="" && ./configure --with-dtrace && make
...
undefined reference to `python_line_semaphore'
...

What about DFFLAGS=" " ?

Nope.

Weird I just tried on ubuntu/systemtap...

$ make clean && make distclean
$ git clean -x
$ export DFLAGS=""
$ export DFFLAGS=""
$ ./configure --with-dtrace && make
...
undefined reference to `python_audit_semaphore'
...

ah sorry I meant DFLAGS=" " (with a space).

If it works for you, it might mean making a specific case for Linux systems in configure.ac as a proper fix.

Oh, my bad.

DFLAGS=" "

^ that indeed works.

New changeset 3c97e1e457033bbb8bbe0b7198bd13fc794a12b0 by Petr Viktorin in branch 'master':
bpo-39761: Fix dtrace build with empty $DFLAGS (GH-18766)
https://github.com/python/cpython/commit/3c97e1e457033bbb8bbe0b7198bd13fc794a12b0