CMake 3.20 breaks 32-bit building on GA CI: finds wrong libraries

The clang-format and both Linux x86 jobs suddenly started failing about an hour ago.

Xref #4780 (closed) where 32-bit apt packages were messed up.

Clang-format says:

Reading Script: /home/runner/work/dynamorio/dynamorio/suite/runsuite.cmake,automated_ci;64_only;require_format
Detected a CI clang suite: disabling running of tests
CMake Error at /home/runner/work/dynamorio/dynamorio/suite/runsuite.cmake:254 (message):
  FATAL ERROR: clang-format is required but not found!

[Ubuntu] Clang, GCC and Gfortran versions less than 9.x will be removed from images on March, 29

Though it still lists clang 9 as being installed in the base.

For the 32-bit the failures look like a messed-up toolchain finding the wrong libraries:

https://github.com/DynamoRIO/dynamorio/pull/4829/checks?check_run_id=2247626216

2021-04-01T16:07:58.4961762Z [  2%] Linking C executable bin/linux.infinite
2021-04-01T16:07:58.4962874Z /usr/lib/x86_64-linux-gnu/libdl.so: error adding symbols: File in wrong format
2021-04-01T16:07:58.4964490Z suite/tests/CMakeFiles/linux.infinite.dir/build.make:98: recipe for target 'suite/tests/bin/linux.infinite' failed
2021-04-01T16:07:58.4966284Z CMakeFiles/Makefile2:7501: recipe for target 'suite/tests/CMakeFiles/linux.infinite.dir/all' failed
2021-04-01T16:07:58.4967132Z collect2: error: ld returned 1 exit status

2021-04-01T16:07:58.4971965Z [  2%] Linking C executable bin/client.mbr_instrumentation_segment
2021-04-01T16:07:58.4973167Z /usr/lib/x86_64-linux-gnu/libdl.so: error adding symbols: File in wrong format
2021-04-01T16:07:58.4974711Z suite/tests/CMakeFiles/client.mbr_instrumentation_segment.dir/build.make:98: recipe for target 'suite/tests/bin/client.mbr_instrumentation_segment' failed

2021-04-01T16:09:28.5436729Z [ 58%] Linking CXX executable ../bin32/prefetch_analyzer_launcher
2021-04-01T16:09:28.5438665Z /usr/lib/x86_64-linux-gnu/libz.so: error adding symbols: File in wrong format
2021-04-01T16:09:28.5440235Z clients/drcachesim/CMakeFiles/prefetch_analyzer_launcher.dir/build.make:120: recipe for target 'clients/bin32/prefetch_analyzer_launcher' failed
2021-04-01T16:09:28.5441277Z collect2: error: ld returned 1 exit status

This breaks 64-bit as well b/c it has one 32-bit build for cross-arch testing:

2021-04-01T16:11:18.1127287Z 8: [100%] Linking C executable bin/linux.execve32
2021-04-01T16:11:18.1128546Z 8: /usr/lib/x86_64-linux-gnu/libdl.so: error adding symbols: File in wrong format
2021-04-01T16:11:18.1129378Z 8: collect2: error: ld returned 1 exit status