32-bit docs failing to build with doxygen 1.8.20

32-bit used to build on this machine, but this is the first attempt after an upgrade in cmake, gcc, and doxygen:

$ rm -rf *; CFLAGS=-m32 CXXFLAGS=-m32 cmake -GNinja -DBUILD_TESTS=ON -DDEBUG=ON ../src && ninja
-- The C compiler identification is GNU 10.2.0
<...>
FAILED: api/docs/html/index.html 
cd /home/bruening/dr/git/build_x86_dbg_tests/api/docs && /usr/bin/cmake -D DOXYGEN_EXECUTABLE=/usr/bin/doxygen -Ddoxygen_ver=1.8.20 -Dversion_number=8.0.18610 "-Dmodule_string_long=\"DynamoRIO Extension Details\"" -Dmodule_string_short=\"Extension\" -Dhome_url=\"http://www.dynamorio.org\" "-Dhome_title=\"DynamoRIO Home Page\"" -Dlogo_imgfile=\"drlogo.png\" -P /home/bruening/dr/git/src/api/docs/CMake_rundoxygen.cmake
CMake Error at /home/bruening/dr/git/src/api/docs/CMake_rundoxygen.cmake:143 (message):
  *** /usr/bin/doxygen failed: ***

  /home/bruening/dr/git/src/api/docs/intro.dox:142: warning: image file
  interpose.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:143: warning: image file
  interpose.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:144: warning: image file
  interpose.eps is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:163: warning: image file
  flow-highlevel.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:164: warning: image file
  flow-highlevel.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:165: warning: image file
  flow-highlevel.eps is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:180: warning: image file
  flow.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:181: warning: image file
  flow.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:182: warning: image file
  flow.eps is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:85: warning: image file
  windows.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:86: warning: image file
  windows.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:87: warning: image file
  windows.eps is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:782: warning: image file
  client.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:783: warning: image file
  client.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/intro.dox:784: warning: image file
  client.eps is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:85: warning: image file
  windows.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:86: warning: image file
  windows.png is not found in IMAGE_PATH: assuming external image.

  /home/bruening/dr/git/src/api/docs/transp.dox:87: warning: image file
  windows.eps is not found in IMAGE_PATH: assuming external image.