Add builder for x86_64-unknown-linux-gnux32 in cross2

Author: malbarbo

src/ci/docker/cross2/Dockerfile

@@ -47,6 +47,7 @@ ENV TARGETS=x86_64-unknown-fuchsia
 ENV TARGETS=$TARGETS,aarch64-unknown-fuchsia
 ENV TARGETS=$TARGETS,sparcv9-sun-solaris
 ENV TARGETS=$TARGETS,x86_64-sun-solaris
+ENV TARGETS=$TARGETS,x86_64-unknown-linux-gnux32
 
 ENV RUST_CONFIGURE_ARGS --target=$TARGETS --enable-extended
 ENV SCRIPT python2.7 ../x.py dist --target $TARGETS

src/tools/build-manifest/src/main.rs

@@ -95,6 +95,7 @@ static TARGETS: &'static [&'static str] = &[
     "x86_64-unknown-freebsd",
     "x86_64-unknown-fuchsia",
     "x86_64-unknown-linux-gnu",
+    "x86_64-unknown-linux-gnux32",
     "x86_64-unknown-linux-musl",
     "x86_64-unknown-netbsd",
     "x86_64-unknown-redox",