Adds an environment to check, how well Linux builds with system packages

A special mode `audacity_obey_system_dependencies` is added, so the build will fail if we could not build against a system package for some reason. 

The following packages are marked for the local build now:

* **wxWidgets**: Ubuntu lacks support for 3.1.3. We can't build against 3.0 branch.
* **portaudio**: there are issues, that prevent using a system version of portaudio.
* **sqlite3**: Ubuntu package is very dated; we care about the performance and stability.
* **nyquist**: Ubuntu has no package available.
* **vamp**: Ubuntu has no development package available.
* **portmixer**: Ubuntu has no package available.
* **sbsms**: Ubuntu package is very dated; we care about the performance and stability.

We use docker to create a clean build environment. Currently, `pkg-config` is used to locate the system libraries. There are few issues with `pkg-config` on Ubuntu:

* It does not work with `lame` and `portmidi`.
* The packaged files for `id3tag` and `mad` have wrong version.
We fix such cases by copying the 
into `/usr/local/lib`.

cmake-proxies/CMakeLists.txt

@@ -5,6 +5,12 @@ cmd_option( ${_OPT}lib_preference
             STRINGS "system" "local"
 )
 
+# Special mode, that will force dependencies to the packages provided by system unless they were set to local explicitly.
+cmd_option( ${_OPT}obey_system_dependencies
+            "Use system packages to satisfy dependencies"
+            Off
+)
+
 # Required libraries
 #
 #       directory          option      symbol      req   chk   version

cmake-proxies/cmake-modules/AudacityFunctions.cmake

@@ -574,6 +574,7 @@ function( addlib dir name symbol required check )
    if( ${use} STREQUAL "system" )
       # Look them up
       pkg_check_modules( PKG_${TARGET} ${packages} )
+
       if( PKG_${TARGET}_FOUND )
          message( STATUS "Using '${name}' system library" )
 
@@ -586,6 +587,8 @@ function( addlib dir name symbol required check )
          # And add it to our target
          target_include_directories( ${TARGET} INTERFACE ${INCLUDES} )
          target_link_libraries( ${TARGET} INTERFACE ${LIBRARIES} )
+      elseif( ${_OPT}obey_system_dependencies )
+         message( FATAL_ERROR "Failed to find the system package ${name}" )
       else()
          set( ${use} "local" )
          set_property( CACHE ${use} PROPERTY VALUE "local" )

linux/build-environment/Dockerfile

@@ -0,0 +1,66 @@
+FROM ubuntu:focal
+
+LABEL maintainer="d.vedenko@audacityteam.org"
+LABEL description="A build environment to check the builds for the package maintainers"
+LABEL version="3.0"
+
+ENV TZ=Europe/London
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
+
+RUN apt-get update
+
+RUN apt-get install -y \
+    build-essential \
+    python3-minimal \
+    python3-pip \
+    g++-9 \
+    libstdc++-9-dev \
+    cmake \
+    git
+
+RUN pip3 install conan
+
+RUN apt-get install -y \ 
+    zlib1g-dev \
+    libgtk2.0-dev \
+    libasound2-dev \
+    libavformat-dev \
+    libjack-jackd2-dev \
+    libexpat1-dev \
+    libmp3lame-dev \
+    libsndfile-dev \
+    libsoxr-dev \
+    portaudio19-dev \
+    libsqlite3-dev \
+    libavcodec-dev \
+    libavformat-dev \
+    libavutil-dev \
+    libid3tag0-dev \
+    libmad0-dev \
+    libvamp-hostsdk3v5 \
+    libogg-dev \
+    libvorbis-dev \
+    libflac-dev \
+    libflac++-dev \
+    lv2-dev \
+    liblilv-dev \
+    libserd-dev \
+    libsord-dev \
+    libsratom-dev \
+    libsuil-dev \
+    libportmidi-dev \
+    libportsmf-dev \
+    libsbsms-dev \
+    libsoundtouch-dev \
+    libtwolame-dev \
+    libssl-dev \
+    libcurl4-openssl-dev
+
+WORKDIR /audacity
+
+COPY ["build_audacity.sh", "/audacity/"]
+
+# pkg-config is so broken
+COPY ["pkgconfig/*", "/usr/local/lib/pkgconfig/"]
+
+CMD ["./build_audacity.sh"]

linux/build-environment/build_audacity.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+
+conan --version
+
+if [ ! -d "audacity" ]
+then
+    git clone https://github.com/audacity/audacity
+fi
+
+mkdir -p build
+
+cd build
+
+cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release \
+    -Daudacity_obey_system_dependencies=On \
+    -Daudacity_use_wxwidgets=local \
+    -Daudacity_use_expat=system \
+    -Daudacity_use_lame=system \
+    -Daudacity_use_sndfile=system \
+    -Daudacity_use_soxr=system \
+    -Daudacity_use_portaudio=local \
+    -Daudacity_use_sqlite=local \
+    -Daudacity_use_ffmpeg=loaded \
+    -Daudacity_use_id3tag=system \
+    -Daudacity_use_mad=system \
+    -Daudacity_use_nyquist=local \
+    -Daudacity_use_vamp=local \
+    -Daudacity_use_ogg=system \
+    -Daudacity_use_vorbis=system \
+    -Daudacity_use_flac=system \
+    -Daudacity_use_lv2=system \
+    -Daudacity_use_midi=system \
+    -Daudacity_use_portmixer=local \
+    -Daudacity_use_portsmf=system \
+    -Daudacity_use_sbsms=local \
+    -Daudacity_use_soundtouch=system \
+    -Daudacity_use_twolame=system \
+    ../audacity
+
+make -j`nproc`
+
+cd bin/Release
+mkdir -p "Portable Settings"
+
+ls -la .

linux/build-environment/pkgconfig/id3tag.pc

@@ -0,0 +1,11 @@
+prefix=/usr
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include
+
+Name: id3tag
+Description: ID3 tag reading library
+Requires:
+Version: 0.15.1b
+Libs: -L${libdir} -lid3tag -lz
+Cflags: -I${includedir}

linux/build-environment/pkgconfig/lame.pc

@@ -0,0 +1,11 @@
+prefix=/usr
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include
+
+Name: lame
+Description: MP3 encoding library
+Requires:
+Version: 3.100
+Libs: -L${libdir} -lmp3lame
+Cflags: -I${includedir}

linux/build-environment/pkgconfig/mad.pc

@@ -0,0 +1,11 @@
+prefix=/usr
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include
+
+Name: mad
+Description: MPEG Audio Decoder
+Requires:
+Version: 0.15.1b
+Libs: -L${libdir} -lmad
+Cflags: -I${includedir}

linux/build-environment/pkgconfig/portmidi.pc

@@ -0,0 +1,11 @@
+prefix=/usr
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include
+
+Name: portmidi
+Description: library for real-time MIDI input/output
+Requires:
+Version: 0.1
+Libs: -L${libdir} -lportmidi
+Cflags: -I${includedir}