[Pkg-rust-maintainers] help required, rustc on raspbian.

[peter green]

I have been trying to update the rustc package in raspbian buster from 1.23.0 to 1.24.1. Unfortunately I am getting the following error.

      Running `/usr/bin/rustc --crate-name build_helper build_helper/lib.rs --crate-type lib --emit=dep-info,link -C debug-assertions=off -C overflow-checks=on -C metadata=bd106bb3930d3382 -C extra-filename=-bd106bb3930d3382 --out-dir '/rustc-1.24.1+dfsg1/build/bootstrap/debug/deps' -C 'incremental=/rustc-1.24.1+dfsg1/build/bootstrap/debug/incremental' -L 'dependency=/rustc-1.24.1+dfsg1/build/bootstrap/debug/deps' --extern 'filetime=/rustc-1.24.1+dfsg1/build/bootstrap/debug/deps/libfiletime-d18e7d8f38ba7fa7.rlib' -C link-args=-Wl,-z,relro '-Zremap-path-prefix-from=/rustc-1.24.1+dfsg1' -Zremap-path-prefix-to=/usr/src/rustc-1.24.1`
error: unknown codegen option: `incremental`

error: Could not compile `build_helper`.

Caused by:
   process didn't exit successfully: `/usr/bin/rustc --crate-name build_helper build_helper/lib.rs --crate-type lib --emit=dep-info,link -C debug-assertions=off -C overflow-checks=on -C metadata=bd106bb3930d3382 -C extra-filename=-bd106bb3930d3382 --out-dir /rustc-1.24.1+dfsg1/build/bootstrap/debug/deps -C incremental=/rustc-1.24.1+dfsg1/build/bootstrap/debug/incremental -L dependency=/rustc-1.24.1+dfsg1/build/bootstrap/debug/deps --extern filetime=/rustc-1.24.1+dfsg1/build/bootstrap/debug/deps/libfiletime-d18e7d8f38ba7fa7.rlib -C link-args=-Wl,-z,relro -Zremap-path-prefix-from=/rustc-1.24.1+dfsg1 -Zremap-path-prefix-to=/usr/src/rustc-1.24.1` (exit code: 101)
warning: build failed, waiting for other jobs to finish...
error: build failed

The rustc source package is only slightly modified compared to the one in Debian (debdiff below)

diff -Nru rustc-1.24.1+dfsg1/debian/architecture.mk rustc-1.24.1+dfsg1/debian/architecture.mk
--- rustc-1.24.1+dfsg1/debian/architecture.mk   2018-03-03 11:23:04.000000000 +0000
+++ rustc-1.24.1+dfsg1/debian/architecture.mk   2018-03-16 00:05:34.000000000 +0000
@@ -2,10 +2,7 @@

  include /usr/share/dpkg/architecture.mk

-rust_cpu = $(subst i586,i686,\
-$(if $(findstring -armhf-,-$(2)-),$(subst arm,armv7,$(1)),\
-$(if $(findstring -armel-,-$(2)-),$(subst arm,armv5te,$(1)),\
-$(1))))
+rust_cpu = $(subst i586,i686,$(1))
  rust_type_setvar = $(1)_RUST_TYPE ?= $(call rust_cpu,$($(1)_GNU_CPU),$($(1)_ARCH))-unknown-$($(1)_GNU_SYSTEM)

  $(foreach machine,BUILD HOST TARGET,\
diff -Nru rustc-1.24.1+dfsg1/debian/changelog rustc-1.24.1+dfsg1/debian/changelog
--- rustc-1.24.1+dfsg1/debian/changelog 2018-03-07 19:07:27.000000000 +0000
+++ rustc-1.24.1+dfsg1/debian/changelog 2018-03-16 00:05:34.000000000 +0000
@@ -1,3 +1,13 @@
+rustc (1.24.1+dfsg1-1+rpi1) buster-staging; urgency=medium
+
+  [changes brought forward from 1.15.1+dfsg1-1~exp3+rpi1 by Peter Michael Green <plugwash at raspbian.org> at Wed, 15 Mar 2017 10:16:18 +0000]
+  * Fix clean target.
+  * Build for armv6.
+  [changes introduced in 1.18.0+dfsg1-4+rpi1 by Peter Michael Green]
+  * Disable testsuite.
+
+ -- Peter Michael Green <plugwash at raspbian.org>  Fri, 16 Mar 2018 00:05:34 +0000
+
  rustc (1.24.1+dfsg1-1) unstable; urgency=medium

    * Upload to unstable.
diff -Nru rustc-1.24.1+dfsg1/debian/rules rustc-1.24.1+dfsg1/debian/rules
--- rustc-1.24.1+dfsg1/debian/rules     2018-03-07 19:06:58.000000000 +0000
+++ rustc-1.24.1+dfsg1/debian/rules     2018-03-16 00:05:34.000000000 +0000
@@ -231,7 +231,7 @@
                 test "$$(stat -c %s "$$x")" -lt 6000000; \
         done
  ifeq (, $(filter nocheck,$(DEB_BUILD_PROFILES)))
-ifeq (, $(filter nocheck,$(DEB_BUILD_OPTIONS)))
+ifeq (testsuitedisabled, $(filter nocheck,$(DEB_BUILD_OPTIONS)))
         $(RUSTBUILD_TEST) --no-fail-fast $(RUSTBUILD_FLAGS) $(RUSTBUILD_TEST_FLAGS) | tee $(TEST_LOG)
         test -f $(TEST_LOG)
         echo "Summary of specific test failures:"; \

Any thoughts on what the problem might be and how to fix it?