Add rust#50789 to fix same-version bootstrap

We don't need to rebuild for this patch now, but it will correct the
FTBFS that Koschei is currently reporting.

0001-Ensure-libraries-built-in-stage0-have-unique-metadat.patch

@@ -0,0 +1,40 @@
+From e8e5eb58c0d6890f73ea01354e18f51b1a6697f8 Mon Sep 17 00:00:00 2001
+From: Josh Stone <jistone@redhat.com>
+Date: Tue, 15 May 2018 17:48:02 -0700
+Subject: [PATCH] Ensure libraries built in stage0 have unique metadata
+
+Issue #50786 shows a case with local rebuild where the libraries built
+by stage0 had the same suffix as stage0's own, and were accidentally
+loaded by that stage0 rustc when compiling `librustc_trans`.
+
+Now we set `__CARGO_DEFAULT_LIB_METADATA` to "bootstrap" during stage0,
+rather than the release channel like usual, so the library suffix will
+always be completely distinct from the stage0 compiler.
+---
+ src/bootstrap/builder.rs | 10 +++++++++-
+ 1 file changed, 9 insertions(+), 1 deletion(-)
+
+diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
+index 17f19222e6ea..e5824010ef2c 100644
+--- a/src/bootstrap/builder.rs
++++ b/src/bootstrap/builder.rs
+@@ -592,7 +592,15 @@ impl<'a> Builder<'a> {
+ 
+         // FIXME: Temporary fix for https://github.com/rust-lang/cargo/issues/3005
+         // Force cargo to output binaries with disambiguating hashes in the name
+-        cargo.env("__CARGO_DEFAULT_LIB_METADATA", &self.config.channel);
++        let metadata = if compiler.stage == 0 {
++            // Treat stage0 like special channel, whether it's a normal prior-
++            // release rustc or a local rebuild with the same version, so we
++            // never mix these libraries by accident.
++            "bootstrap"
++        } else {
++            &self.config.channel
++        };
++        cargo.env("__CARGO_DEFAULT_LIB_METADATA", &metadata);
+ 
+         let stage;
+         if compiler.stage == 0 && self.local_rebuild {
+-- 
+2.17.0
+

rust.spec

@@ -72,6 +72,9 @@ Source0:        https://static.rust-lang.org/dist/%{rustc_package}.tar.xz
 # https://github.com/rust-lang/rust/pull/49959
 Patch1:         pull-49959.patch
 
+# https://github.com/rust-lang/rust/pull/50789/
+Patch2:         0001-Ensure-libraries-built-in-stage0-have-unique-metadat.patch
+
 # Get the Rust triple for any arch.
 %{lua: function rust_triple(arch)
   local abi = "gnu"
@@ -372,6 +375,7 @@ test -f '%{local_rust_root}/bin/rustc'
 %setup -q -n %{rustc_package}
 
 %patch1 -p1
+%patch2 -p1
 
 %if "%{python}" == "python3"
 sed -i.try-py3 -e '/try python2.7/i try python3 "$@"' ./configure