Make partial RELRO default on ppc64 due to segfault

On at least RHEL6 there is a segfault caused by the older ld.so version
when BIND_NOW is used, so use partial RELRO by default on ppc64
architectures for now.

Signed-off-by: Johannes Löthberg <johannes@kyriasis.com>

src/librustc_back/target/powerpc64_unknown_linux_gnu.rs

@@ -9,14 +9,18 @@
 // except according to those terms.
 
 use LinkerFlavor;
-use target::{Target, TargetResult};
+use target::{Target, TargetResult, RelroLevel};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_base::opts();
     base.cpu = "ppc64".to_string();
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
     base.max_atomic_width = Some(64);
 
+    // ld.so in at least RHEL6 on ppc64 has a bug related to BIND_NOW, so only enable partial RELRO
+    // for now. https://github.com/rust-lang/rust/pull/43170#issuecomment-315411474
+    base.relro_level = RelroLevel::Partial;
+
     // see #36994
     base.exe_allocation_crate = None;