add_conan_lib cmake function is defined, that allows to add a dependency using Conan with two possible system fallbacks:
1. pkg_check_modules is invoked, if `PGK_CONFIG ...` is present
2. find_package is invoked if `FIND_PACKAGE_OPTIONS` is present and `pkg_check_modules` has failed
If `ALWAYS_ALLOW_CONAN_FALLBACK` is present - `obey_system_dependencies` will be ignored for the package
Currently, the following dependencies are retrieved using Conan:
* zlib
* expat
* wxwidgets
* libmp3lame
* libid3tag
* libmad
The last three libraries are included in this commit, as they depend on zlib.
Properly pass **arch** and **os.version** to Conan
Since XCode 10, Apple does not recommend building for macOS <10.9
Reason - 10.7 and 10.8 require libstdc++
We enforce libc++
```# Shouldn't cmake do this???
string( APPEND CMAKE_CXX_FLAGS " -stdlib=libc++" )```
While this generally works, it makes the proper dependency management tricky.
Compiler message for the library support:
```
clang: warning: libstdc++ is deprecated; move to libc++ with a minimum deployment target of OS X 10.9 [-Wdeprecated]
ld: library not found for -lstdc++
```
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`.
