Setup cross compiling using the cross project (tgstation#70)

Cross.toml

@@ -0,0 +1,11 @@
+[target.i686-pc-windows-gnu]
+image = "rustembedded/cross:i686-pc-windows-gnu"
+
+[target.i686-unknown-linux-gnu]
+image = "rustg/i686-unknown-linux-gnu"
+
+[build.env]
+passthrough = [
+	"PKG_CONFIG_ALLOW_CROSS"
+]
+

docker/Dockerfile.i686-unknown-linux-gnu

@@ -0,0 +1,5 @@
+FROM rustembedded/cross:i686-unknown-linux-gnu
+
+RUN dpkg --add-architecture i386 && \
+	apt-get update && \
+	apt-get install --assume-yes zlib1g-dev:i386 libssl-dev:i386 pkg-config:i386

scripts/prepare_binaries.sh

@@ -3,16 +3,18 @@ set -euo pipefail
 
 touch build.rs
 
+echo '==== Make sure cross is installed ===='
+cargo install cross
+
 echo '==== Linux build ====' # ------------------------------------------------
 rustup target add i686-unknown-linux-gnu
 env PKG_CONFIG_ALLOW_CROSS=1 \
-    cargo build --release --target i686-unknown-linux-gnu
+	cargo build --release --target i686-unknown-linux-gnu
 
 mv target/rust_g.dm target/rust_g.linux.dm
 
 echo '==== Windows build ====' # ----------------------------------------------
-rustup target add i686-pc-windows-gnu
-cargo build --release --target i686-pc-windows-gnu
+cross build --release --target i686-pc-windows-gnu
 # https://github.com/rust-lang/rust/issues/12859#issuecomment-62255275
 # Most distros ship 32-bit toolchains with SJLJ unwinding, but for 32-bit Rust
 # can only cross-compile targeting DWARF. All 64-bit toolchains use SEH, where
@@ -27,6 +29,10 @@ cargo build --release --target i686-pc-windows-gnu
 # tar xf rust-mingw-nightly-i686-pc-windows-gnu.tar.gz
 # ./rust-mingw-nightly-i686-pc-windows-gnu/install.sh --prefix=$(rustc --print sysroot)
 
+# Luckily we are taking the third workaround, which is using the cross projects i686
+# windows toolchain docker which comes with an updated version of mingw that supports
+# the DWARF based unwinding, freeing us from such earthly concerns
+
 # Make sure the `rust_g.dm` produced for each platform are the same, just in
 # case.
 cmp target/rust_g.dm target/rust_g.linux.dm