Lagom: Add two-stage build for Fuzzers to enable fuzzing generated code

This allows us to fuzz the generated unicode and timezone database
helpers, and to fuzz things like LibJS using Fuzzilli to get proper
coverage of our unicode handling code.

Update the Azure CI to use the new two-stage build as well, and cleanup
some unused CMake options there.

Meta/Lagom/BuildFuzzers.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+set -e
+
+BEST_CLANG_CANDIDATE=""
+
+die() {
+    >&2 echo "die: $*"
+    exit 1
+}
+
+pick_clang() {
+    local BEST_VERSION=0
+    for CLANG_CANDIDATE in clang clang-13 clang-14 /usr/local/bin/clang-13 /usr/local/bin/clang-14; do
+        if ! command -v $CLANG_CANDIDATE >/dev/null 2>&1; then
+            continue
+        fi
+        if $CLANG_CANDIDATE --version 2>&1 | grep "Apple clang" >/dev/null; then
+            continue
+        fi
+        if ! $CLANG_CANDIDATE -dumpversion >/dev/null 2>&1; then
+            continue
+        fi
+        local VERSION=""
+        VERSION="$($CLANG_CANDIDATE -dumpversion)"
+        local MAJOR_VERSION="${VERSION%%.*}"
+        if [ "$MAJOR_VERSION" -gt "$BEST_VERSION" ]; then
+            BEST_VERSION=$MAJOR_VERSION
+            BEST_CLANG_CANDIDATE="$CLANG_CANDIDATE"
+        fi
+    done
+    if [ "$BEST_VERSION" -lt 13 ]; then
+        die "Please make sure that Clang version 13 or higher is installed."
+    fi
+}
+
+# Save flags for oss-fuzz to avoid fuzzing Tools/
+# https://google.github.io/oss-fuzz/getting-started/new-project-guide/#temporarily-disabling-code-instrumentation-during-builds
+CFLAGS_SAVE="$CFLAGS"
+CXXFLAGS_SAVE="$CXXFLAGS"
+unset CFLAGS
+unset CXXFLAGS
+export AFL_NOOPT=1
+
+# FIXME: Replace these CMake invocations with a CMake superbuild?
+echo "Building Lagom Tools..."
+cmake -GNinja -B Build/tools \
+    -DBUILD_LAGOM=OFF \
+    -DCMAKE_INSTALL_PREFIX=Build/tool-install
+ninja -C Build/tools install
+
+# Restore flags for oss-fuzz
+export CFLAGS="${CFLAGS_SAVE}"
+export CXXFLAGS="${CXXFLAGS_SAVE}"
+unset AFL_NOOPT
+
+echo "Building Lagom Fuzzers..."
+
+if [ "$#" -gt "0" ] && [ "--oss-fuzz" = "$1" ] ; then
+    echo "Building for oss-fuzz configuration..."
+    cmake -GNinja -B Build/fuzzers \
+        -DBUILD_LAGOM=ON \
+        -DBUILD_SHARED_LIBS=OFF \
+        -DENABLE_OSS_FUZZ=ON \
+        -DCMAKE_C_COMPILER="$CC" \
+        -DCMAKE_CXX_COMPILER="$CXX" \
+        -DCMAKE_CXX_FLAGS="$CXXFLAGS -DOSS_FUZZ=ON" \
+        -DLINKER_FLAGS="$LIB_FUZZING_ENGINE" \
+        -DCMAKE_PREFIX_PATH=Build/tool-install
+    ninja -C Build/fuzzers
+    cp Build/fuzzers/Fuzzers/Fuzz* "$OUT"/
+else
+    echo "Building for local fuzz configuration..."
+    pick_clang
+    cmake -GNinja -B Build/lagom-fuzzers \
+        -DBUILD_LAGOM=ON \
+        -DENABLE_FUZZER_SANITIZER=ON \
+        -DENABLE_ADDRESS_SANITIZER=ON \
+        -DENABLE_UNDEFINED_SANITIZER=ON \
+        -DCMAKE_PREFIX_PATH=Build/tool-install \
+        -DCMAKE_C_COMPILER=$BEST_CLANG_CANDIDATE \
+        -DCMAKE_CXX_COMPILER="${BEST_CLANG_CANDIDATE/clang/clang++}"
+    ninja -C Build/lagom-fuzzers
+fi