Starting with LLVM 12 and GCC 11 (and backported to gcc-10 for Debian),
GCC introduces optimizations for new micro-architecture levels from
the x86-64 psABI.  Filing these bug reports for packages building with
the current level (x86-64), but not with x86-64-v3.

To reproduce these issues, append -march=x86-64-v3 to the compiler
flags (CFLAGS, CXXFLAGS, ...).  You also need hardware supporting these.
The easiest way is to call the dynamic linker in glibc 2.33 like
  /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 --help
Otherwise look at the flags in /proc/cpuinfo and compare these with
those from table 3.1 in the System V Application Binary Interface doc:
https://gitlab.com/x86-psABIs/x86-64-ABI/-/wikis/x86-64-psABI

Please don't upload a package setting these flags by default.  The
x86-64 baseline is still unchanged.

The full build log can be found at:
http://people.debian.org/~doko/logs/20210228/filtered/gcc10-v3/teem_1.12.0~20160122-4_unstable_gcc10-v3.log
The last lines of the build log are at the end of this report.

[...]
      Start 18: macros
15/37 Test #17: sanity ...........................   Passed    0.00 sec
      Start 19: bspec
16/37 Test #19: bspec ............................   Passed    0.00 sec
      Start 20: unulist
17/37 Test #20: unulist ..........................   Passed    0.01 sec
      Start 21: stackBlurParm
18/37 Test #21: stackBlurParm ....................   Passed    0.00 sec
      Start 22: probeScl
19/37 Test #16: tskip10n .........................   Passed    0.06 sec
      Start 23: probePolynomial
20/37 Test #22: probeScl .........................   Passed    0.11 sec
      Start 24: probeMulti
21/37 Test #18: macros ...........................   Passed    0.16 sec
      Start 25: tendlist
22/37 Test #25: tendlist .........................   Passed    0.01 sec
      Start 26: glyphBqd
23/37 Test #26: glyphBqd .........................   Passed    0.01 sec
      Start 27: enmall
24/37 Test #27: enmall ...........................   Passed    0.03 sec
      Start 28: kernall
25/37 Test  #2: misc .............................   Passed    0.37 sec
      Start 29: buildinfo
26/37 Test #29: buildinfo ........................   Passed    0.00 sec
      Start 30: probeSS_box01
27/37 Test #30: probeSS_box01 ....................   Passed    0.36 sec
      Start 31: probeSS_cos01
28/37 Test #31: probeSS_cos01 ....................   Passed    0.37 sec
      Start 32: probeSS_cos02
29/37 Test #32: probeSS_cos02 ....................   Passed    0.41 sec
      Start 33: probeSS_cos04
30/37 Test #33: probeSS_cos04 ....................   Passed    0.61 sec
      Start 34: probeSS_cos10
31/37 Test #23: probePolynomial ..................   Passed    2.48 sec
      Start 35: probeSS_ctmr02
32/37 Test #35: probeSS_ctmr02 ...................   Passed    0.44 sec
      Start 36: probeSS_ctmr04
33/37 Test #36: probeSS_ctmr04 ...................***Failed    0.33 sec
kpack = ctmrsup, ctmrsupD, ctmrsupDD
/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/bin/test_probeSS: trouble (orig, orig):
[probeSS] probeTask1: on point 0 of kindIdx 0
[probeSS] multiAnswerCompare: man1->san[si] 1.2261255947091414e-06 != man2->san[si] 1.2261255947091416e-06

      Start 37: probeSS_ctmr10
34/37 Test #24: probeMulti .......................   Passed    3.30 sec
35/37 Test #37: probeSS_ctmr10 ...................***Failed    0.32 sec
kpack = ctmrsup, ctmrsupD, ctmrsupDD
/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/bin/test_probeSS: trouble (orig, orig):
[probeSS] probeTask1: on point 0 of kindIdx 0
[probeSS] multiAnswerCompare: man1->san[si] 8.8328547952638039e-07 != man2->san[si] 8.832854795263805e-07

36/37 Test #28: kernall ..........................   Passed    3.80 sec
37/37 Test #34: probeSS_cos10 ....................   Passed    2.09 sec

95% tests passed, 2 tests failed out of 37

Total Test time (real) =   4.21 sec

The following tests FAILED:
	 36 - probeSS_ctmr04 (Failed)
	 37 - probeSS_ctmr10 (Failed)
Errors while running CTest
make[2]: *** [Makefile:129: test] Error 8
make[2]: Leaving directory '/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu'
	rm -fr -- /tmp/dh-xdg-rundir-OcZWeHFb
dh_auto_test: error: cd obj-x86_64-linux-gnu && make -j4 test LD_LIBRARY_PATH=/<<BUILDDIR>>/teem-1.12.0\~20160122/obj-x86_64-linux-gnu/bin:D_LIBRARY_PATH ARGS\+=-j4 returned exit code 2
make[1]: *** [debian/rules:39: override_dh_auto_test] Error 25
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
make: *** [debian/rules:32: binary] Error 2
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2