Add Dockerfile and GH workflow for Arch Linux

Apart from having a CI for yet another flavour of Linux, I wanted to see
whether I can reproduce the failure reported in #39. That's not the
case, so I suggest that we close #39.

.github/workflows/docker-archlinux.yml

@@ -0,0 +1,16 @@
+name: docker-archlinux
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build the Docker image
+        run: docker build . --file Dockerfile_archlinux --tag llvm-tutor:llvm-12

Dockerfile_archlinux

@@ -0,0 +1,47 @@
+# =============================================================================
+# An Arch Linux docker file for llvm-tutor. Clones and builds llvm-tutor, runs
+# all tests. It uses the precompiled LLVM packages from Fedora.
+#
+# USAGE:
+# ```bash
+# wget https://raw.githubusercontent.com/banach-space/llvm-tutor/main/Dockerfile_archlinux
+# docker build -t=llvm-tutor:llvm-12 .
+# docker run --rm -it --hostname=llvm-tutor llvm-tutor:llvm-12 /bin/bash
+# ```
+# =============================================================================
+
+FROM archlinux
+
+ENV LLVM_DIR /usr/
+ENV TUTOR_DIR /llvm-tutor
+
+# 1. INSTALL DEPENDENCIES
+RUN pacman -Syu --noconfirm \
+    git \
+    cmake \
+    ninja \
+    gcc \
+    llvm \
+    clang \
+    python-pip
+
+# 2. INSTALL LIT
+RUN pip3 install lit
+
+# 3. CLONE LLVM-TUTOR
+RUN git clone https://github.com/banach-space/llvm-tutor $TUTOR_DIR
+
+# 4. BUILD AND RUN HELLO-WORLD
+RUN mkdir -p $TUTOR_DIR/hello-world-build \
+    && cd $TUTOR_DIR/hello-world-build \
+    && cmake -G Ninja -DLT_LLVM_INSTALL_DIR=$LLVM_DIR ../HelloWorld \
+    && ninja
+RUN cd $TUTOR_DIR/hello-world-build && $LLVM_DIR/bin/clang -S -O1 -emit-llvm ../inputs/input_for_hello.c -o input_for_hello.ll
+RUN cd $TUTOR_DIR/hello-world-build && $LLVM_DIR/bin/opt -load-pass-plugin ./libHelloWorld.so -passes=hello-world -disable-output input_for_hello.ll 2>&1 | grep "(llvm-tutor) Hello from: foo"
+
+# 5. BUILD AND RUN LLVM-TUTOR
+RUN mkdir -p $TUTOR_DIR/build \
+    && cd $TUTOR_DIR/build \
+    && cmake -G Ninja -DLT_LLVM_INSTALL_DIR=$LLVM_DIR ../ \
+    && ninja \
+    && lit test/