Add 32 bit headers in .travis.yml

Author: Owen Jones

.travis.yml

@@ -70,6 +70,7 @@ jobs:
             - g++-5
             - libubsan0
             - python3-pip
+            - libc6-dev-i386
       before_install:
         - mkdir bin ; ln -s /usr/bin/gcc-5 bin/gcc
           # Install pytest locally and adjust PATH so pip3 can find it
@@ -137,6 +138,7 @@ jobs:
             - libubsan0
             - parallel
             - python3-pip
+            - libc6-dev-i386
       before_install:
         - mkdir bin ; ln -s /usr/bin/gcc-5 bin/gcc
           # Install pytest locally and adjust PATH so pip3 can find it
@@ -171,6 +173,7 @@ jobs:
             - libubsan0
             - parallel
             - python3-pip
+            - libc6-dev-i386
       before_install:
         - mkdir bin ; ln -s /usr/bin/clang-3.7 bin/gcc
         - export CCACHE_CPP2=yes
@@ -203,6 +206,7 @@ jobs:
             - libstdc++-5-dev
             - libubsan0
             - python3-pip
+            - libc6-dev-i386
       before_install:
         - mkdir bin ; ln -s /usr/bin/clang-3.7 bin/gcc
         - export CCACHE_CPP2=yes