Revert previous target-dir change

This doesn't actually work without some seriously hacky workarounds. A
proper solution involves placing everything in one cargo workspace. That
won't be practical until custom profiles are available (since the
native library/binary require panic=unwind and the rel requires
panic=abort) (see rust-lang/cargo#6988 for progress on that)

compile_to_ppc/.cargo/config

@@ -1,5 +1,2 @@
-[build]
-target-dir = "../target"
-
 [target.powerpc-unknown-linux-gnu]
 rustflags = ["-C", "relocation-model=static", "-C", "target-cpu=750"]

generated/rel_files/build.rs

@@ -29,7 +29,7 @@ fn invoke_cargo(ppc_manifest: &Path, package: &str)
         .arg("-C")
         .arg("target-cpu=750")
         .env("RUSTC_BOOTSTRAP", "1")
-        .env("CARGO_TARGET_DIR", "../../target")
+        .env("CARGO_TARGET_DIR", "../../compile_to_ppc/target")
         .output()
         .expect("Failed to compile ppc crate");
     if !output.status.success() {
@@ -49,6 +49,7 @@ fn main()
     let ppc_manifest = ppc_dir.join("Cargo.toml");
     let target_dir = ppc_dir
         .join("..")
+        .join("compile_to_ppc")
         .join("target")
         .join("powerpc-unknown-linux-gnu")
         .join("release");