Let's try using Linxu MinGW-w64.

azure-pipelines.yml

@@ -13,16 +13,16 @@ jobs:
   steps:
   - template: azure-pipelines/setup-python3.yml
   - template: azure-pipelines/install-latest-meson.yml
-  - template: azure-pipelines/linux-386-install-gtk-dev-ninja.yml
+  - script: sudo apt-get install ninja-build
   - template: azure-pipelines/configure.yml
     parameters:
-      beforeConfigure: export CFLAGS=-m32 CXXFLAGS=-m32 PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig
       defaultLibrary: static
+      extraOptions: --cross-file=azure-pipelines/cross-386-mingw.txt
   - template: azure-pipelines/build.yml
-  - template: azure-pipelines/artifacts.yml
+#  - template: azure-pipelines/artifacts.yml
-    parameters:
+#    parameters:
-      os: linux
+#      os: linux
-      arch: 386
+#      arch: 386
-      libtype: static
+#      libtype: static
-      libfiles: libui.a
+#      libfiles: libui.a
-      osHeader: ui_unix.h
+#      osHeader: ui_unix.h

azure-pipelines/configure.yml

@@ -3,9 +3,10 @@
 parameters:
   beforeConfigure: ''
   defaultLibrary: 'must-be-set'
+  extraOptions: ''
 
 steps:
 - script: |
     ${{ parameters.beforeConfigure }}
-    meson setup build --buildtype=release --default-library=${{ parameters.defaultLibrary }}
+    meson setup build --buildtype=release --default-library=${{ parameters.defaultLibrary }} ${{ parameters.extraOptions }}
   displayName: 'Configure'

azure-pipelines/cross-386-mingw.txt

@@ -0,0 +1,16 @@
+[binaries]
+c = '/usr/bin/i686-w64-mingw32-gcc-win32'
+cpp = '/usr/bin/i686-w64-mingw32-g++-win32'
+ar = '/usr/bin/i686-w64-mingw32-gcc-ar-win32'
+strip = '/usr/bin/i686-w64-mingw32-strip'
+pkgconfig = '/usr/bin/i686-w64-mingw32-pkg-config'
+windres = '/usr/bin/i686-w64-mingw32-windres'
+
+[properties]
+root = '/usr/i686-w64-mingw32'
+
+[host_machine]
+system = 'windows'
+cpu_family = 'x86'
+cpu = 'i686'
+endian = 'little'