Add FreeBSD to CI (#8261)

* CI: add FreeBSD job

* CI: add FreeBSD job on CirrusCI

* CI: disable Travis on FreeBSD due to broken ccache

.ci/build-freebsd.sh

@@ -0,0 +1,35 @@
+#!/bin/sh -ex
+
+ccache -s # debug
+
+# Pull all the submodules except llvm
+# Note: Tried to use git submodule status, but it takes over 20 seconds
+# shellcheck disable=SC2046
+git submodule -q update --init $(awk '/path/ && !/llvm/ { print $3 }' .gitmodules)
+
+# XXX Drop after Travis upgrades FreeBSD to 12.2 (see also .ci/install-freebsd.sh)
+case $(${CXX:-c++} --version) in
+    *version\ 8.0.*)
+	fetch https://github.com/llvm/llvm-project/releases/download/llvmorg-10.0.0/libcxx-10.0.0.src.tar.xz
+	tar xf libcxx-10.0.0.src.tar.xz
+	export CC=clang10 CXX=clang++10
+	export CXXFLAGS="$CXXFLAGS -nostdinc++ -isystem $PWD/libcxx-10.0.0.src/include"
+	;;
+esac
+
+CONFIGURE_ARGS="
+	-DCMAKE_C_COMPILER_LAUNCHER=ccache
+	-DCMAKE_CXX_COMPILER_LAUNCHER=ccache
+	-DWITH_LLVM=OFF
+	-DUSE_PRECOMPILED_HEADERS=OFF
+	-DUSE_NATIVE_INSTRUCTIONS=OFF
+	-DUSE_SYSTEM_FFMPEG=ON
+	-DUSE_SYSTEM_CURL=ON
+	-DUSE_SYSTEM_LIBPNG=ON
+"
+
+# shellcheck disable=SC2086
+cmake -B build -G Ninja $CONFIGURE_ARGS
+cmake --build build
+
+ccache -s # debug

.ci/install-freebsd.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env -S su -m root -ex
+# NOTE: this script is run under root permissions
+# shellcheck shell=sh disable=SC2096
+
+# RPCS3 often needs recent Qt5 and Vulkan-Headers
+sed -i '' 's/quarterly/latest/' /etc/pkg/FreeBSD.conf
+
+export ASSUME_ALWAYS_YES=true
+pkg info # debug
+
+# XXX Drop after Travis upgrades FreeBSD to 12.2 (see also .ci/build-freebsd.sh)
+case $(${CXX:-c++} --version) in
+    *version\ 8.0.*)
+	pkg install llvm10
+	;;
+esac
+
+# Mandatory dependencies (qt5-dbus and qt5-gui are pulled via qt5-widgets)
+pkg install git ccache cmake ninja qt5-qmake qt5-buildtools qt5-widgets qt5-concurrent glew openal-soft ffmpeg
+
+# Optional dependencies (libevdev is pulled by qt5-gui)
+pkg install pkgconf alsa-lib pulseaudio sdl2 evdev-proto vulkan-headers vulkan-loader