This is gleaned from Apple: http://lists.apple.com/archives/unix-porting/2003/Dec/msg00107.html
[A non-virtual thunk is] an internal implementation detail used for C++ class hierarchies that involve multiple inheritance. You aren’t doing anything wrong; this is a compiler bug. We know that we need to fix it. In the mean time, the best workaround we know of is to use the same optimization level for linking against a library that you used to compile the library.
(You might also consider not exporting a C++ interface from a library. We work very hard to make sure that the C and Objective C ABI stays the same from one compiler release to the next, but we make no such promise for C++.)
That’s probably no help, but it is an indication of something deeper. I think you may be building wxWidgets incorrectly???
I just build 3.0.2 to see if it would build. Configured wxWidgets 3.0.2 for `x86_64-apple-darwin15.4.0’
Just FYI, I can compile most of Audacity on my Mac mini with XCodebuild. However - I have wxWidgets compiled and lives in
/Users/robert/src/wxWidgets-3.1.0 with a path variable pointing to it.
I compiled it with xcodebuild.
How I’m getting there - briefly.
I downloaded wxWidgets-3.1.0.
It’s on github - see their docs here.
https://github.com/wxWidgets/wxWidgets/blob/v3.1.0/docs/readme.txt
The install.txt that is needed to be followed is in wxWidgets-3.1.0/docs/osx/install.txt in your Widgets src code folder. Probably the same in 3.0.2
You need to follow its instruction, what ever your version. You also don’t need to INSTALL it. Just make it. and point to the folder in your path.
It’s too simple. Like this.
After Xcode is installed, download wxWidgets-{version}.tar.bz2 and then
double-click on it to unpack it to create a wxWidgets directory.
Next use Terminal (under Applications, Utilities, Terminal) to access a command
prompt. Use cd to change directories to your wxWidgets directory and execute
the following sets of commands from the wxWidgets directory.
mkdir build-cocoa-debug
cd build-cocoa-debug
…/configure --enable-debug
make
Build the samples and demos
cd samples; make;cd …
cd demos; make;cd …
After the compilation completes, use Finder to run the samples and demos
Go to build-cocoa-debug/samples to experiment with the Cocoa samples.
Go to build-cocoa-debug/demos to experiment with the Cocoa demos.
Double-click on the executables which have an icon showing three small squares.
The source code for the samples is in wxWidgets/samples
The source code for the demos is in wxWidgets/demos
My Audacity soruce code is in /Users/robert/src/AudacityMASTER - a git pull from Audacity.
Now remember - I’m NOT using the “supported” build elements. Neither wxWidgts, not XCode. I’m using XCode 7.3, with MacOSX10.11.sdk, on OSX 10.11.4.
… so I know it wont build all the way yet. I’m working on it… 
But I do get most of the way with.
codebuild -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk clean -configuration Release 2>&1 | tee clean.log
xcodebuild -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -configuration Release install 2>&1 | tee release.log
Can I shorten this ?
I believe you are possibly not building wxWidgets correctly in the first place. See above.
Your errors are wxWidget errors - not Audacity errors.
oh and yes, I know it all builds and works if I use the “supported” parts of the equation. I’ve done it. I’m working a little ahead of that though…
I hope I am helping and not just making matters worse …
let us know how you get on.
Robert