Try to speed up the build process by consolidating all the apt-get installs into one. These 386 binaries do work, at least.

_travis_yml

@@ -1,35 +1,4 @@
 
-include: &toolchain_linux_386
-  os: linux
-  dist: trusty
-  addons:
-    apt:
-      packages:
-        - ninja-build
-        - gcc-multilib
-        - g++-multilib
-        - libgtk-3-dev:i386
-        # the rest fixes broken dependencies of libgtk:i386
-        - libgirepository-1.0-1:i386
-        - libglib2.0-dev:i386
-        - gir1.2-glib-2.0:i386
-        - gir1.2-atk-1.0:i386
-        - libatk1.0-dev:i386
-        - libfreetype6-dev:i386
-        - libfontconfig1-dev:i386
-        - libcairo2-dev:i386
-        - libgdk-pixbuf2.0-dev:i386
-        - libpango1.0-dev:i386
-        - libxft-dev:i386
-        - libpng12-dev:i386
-
-install:
-  - if [[ "${arch}" == "386" ]]; then
-      export CFLAGS=-m32;
-      export CXXFLAGS=-m32;
-      export PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig;
-    fi
-
 deploy:
   provider: releases
   api_key:

azure-pipelines/linux-386-install-gtk-dev-ninja.yml

@@ -4,13 +4,14 @@
 
 steps:
 - script: |
-    sudo dpkg --add-architecture i386
-    sudo apt-get update
-    sudo apt-get install gcc-multilib g++-multilib || echo 1 # libc6-i386 libc6-dev-i386 lib32stdc++6 lib32tinfo5 lib32tinfo-dev lib32z1 lib32z1-dev
     # Azure Pipelines ships with a patched version of this and that patch is only available on 64-bit systems, so trying to install the 32-bit versions will remove the 64-bit versions outright
     # This is a dependency of Mesa, so we'll have to downgrade to the stock distro ones :/
     llvmPackages=
     for i in libllvm6.0 clang-6.0 libclang-common-6.0-dev liblldb-6.0 liblldb-6.0-dev lld-6.0 lldb-6.0 llvm-6.0-dev python-lldb-6.0 libclang1-6.0 llvm-6.0 llvm-6.0-runtime; do llvmPackages="$llvmPackages $i=1:6.0-1ubuntu2~16.04.1"; done
-    sudo apt-get install --allow-downgrades $llvmPackages
+    sudo dpkg --add-architecture i386
-    sudo apt-get install libgtk-3-dev:i386 ninja-build
+    sudo apt-get update
+    sudo apt-get install --allow-downgrades \
+      gcc-multilib g++-multilib \
+      $llvmPackages \
+      libgtk-3-dev:i386 ninja-build
   displayName: 'Install GTK+ Dev Files and Ninja'