CI: Remove llvm-8 from the Debian Stretch container

For similar reasons to c/s a6b1e2b80f.  While this container is still
build-able for now, all the other problems with explicitly-versioned compilers
remain.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 7a29837572)

automation/build/debian/stretch-llvm-8.list

@@ -1,3 +0,0 @@
-# Strech LLVM 8 repos
-deb http://apt.llvm.org/stretch/ llvm-toolchain-stretch-8 main
-deb-src http://apt.llvm.org/stretch/ llvm-toolchain-stretch-8 main

automation/build/debian/stretch.dockerfile

@@ -49,15 +49,3 @@ RUN apt-get update && \
         apt-get autoremove -y && \
         apt-get clean && \
         rm -rf /var/lib/apt/lists* /tmp/* /var/tmp/*
-
-RUN wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
-COPY stretch-llvm-8.list /etc/apt/sources.list.d/
-
-RUN apt-get update && \
-    apt-get --quiet --yes install \
-        clang-8 \
-        lld-8 \
-        && \
-        apt-get autoremove -y && \
-        apt-get clean && \
-        rm -rf /var/lib/apt/lists* /tmp/* /var/tmp/*

automation/gitlab-ci/build.yaml

@@ -26,13 +26,6 @@
     CXX: clang++
     clang: y
 
-.clang-8-tmpl:
-  variables: &clang-8
-    CC: clang-8
-    CXX: clang++-8
-    LD: ld.lld-8
-    clang: y
-
 .x86-64-build-tmpl:
   <<: *build
   variables:
@@ -97,16 +90,6 @@
   variables:
     <<: *clang
 
-.clang-8-x86-64-build:
-  extends: .x86-64-build
-  variables:
-    <<: *clang-8
-
-.clang-8-x86-64-build-debug:
-  extends: .x86-64-build-debug
-  variables:
-    <<: *clang-8
-
 .clang-x86-32-build:
   extends: .x86-32-build
   variables:
@@ -226,16 +209,6 @@ debian-stretch-clang-debug:
   variables:
     CONTAINER: debian:stretch
 
-debian-stretch-clang-8:
-  extends: .clang-8-x86-64-build
-  variables:
-    CONTAINER: debian:stretch
-
-debian-stretch-clang-8-debug:
-  extends: .clang-8-x86-64-build-debug
-  variables:
-    CONTAINER: debian:stretch
-
 debian-stretch-gcc:
   extends: .gcc-x86-64-build
   variables: