Comment 97 for bug 1750937

14.04 here as well. I didn't try purging the PPA, so I don't know if that works, but what I did was the following:

1. disable the PPA (and sudo apt update)

2. Synaptic refused to apply the changes, so:

$ sudo apt install gcc-4.9-base=4.9.3-0ubuntu4 lib32gcc1=1:4.9.3-0ubuntu4 gcc-4.9-base:i386=4.9.3-0ubuntu4 libmpfr4=3.1.2-1 libcloog-isl4=0.18.2-1 gcc-4.8-base=4.8.4-2ubuntu1~14.04.4 gcc-4.8-base:i386=4.8.4-2ubuntu1~14.04.4 cpp-4.8=4.8.4-2ubuntu1~14.04.4 gcc-4.8=4.8.4-2ubuntu1~14.04.4 libatomic1=4.8.4-2ubuntu1~14.04.4 libasan0=4.8.4-2ubuntu1~14.04.4 libgcc-4.8-dev=4.8.4-2ubuntu1~14.04.4 libgomp1=4.8.4-2ubuntu1~14.04.4 libgfortran3=4.8.4-2ubuntu1~14.04.4 libquadmath0=4.8.4-2ubuntu1~14.04.4 libitm1=4.8.4-2ubuntu1~14.04.4 libtsan0=4.8.4-2ubuntu1~14.04.4 libstdc++6=4.8.4-2ubuntu1~14.04.4 libstdc++6:i386=4.8.4-2ubuntu1~14.04.4 libgcc1=1:4.9.3-0ubuntu4 libgcc1:i386=1:4.9.3-0ubuntu4

...should list 21 packages to install, none to remove.

3. for good measure, reinstall the kernel (4.4.0-119 came out in the meantime) and the nVidia driver

4. reboot

5. $ modinfo nvidia-xxx -k 4.4.0-11x-generic | grep vermagic
...should return retpoline at the end (just replace the x's with your specific versions).