Add UBSAN to ASAN builds

[argilo]

Adding the Undefined Behaviour Sanitizer (UBSAN) to ASAN builds will allow more bugs to be uncovered. I already found a number of bugs this way:

• Fix undefined behaviour in volk_8u_x4_conv_k7_r2_8u #660
• Fix undefined behaviour in volk_32u_reverse_32u #664
• Undefined Behaviour in volk_8u_x4_conv_k7_r2_8u #674
• Generate random integers with uniform_int_distribution #677

[jdemel]

This changes runtime behavior. A quick search indicated that this change may affect performance. Do we want this to happen? Maybe it is sufficient to add a CI test with this option enabled.

[argilo]

ASAN changes runtime behaviour and reduces performance in the same way; it's only meant to be used for finding bugs. The intent here is to add more checks so that more bugs can be caught. I think that's compatible with the intent of #192, which added an ASAN build type in the first place, and seems to have been aimed at finding bugs by hand.

Running CI tests with ASAN+UBSAN at least once for each platform we care about (x86, ARM) would definitely help catch more bugs. The UBSAN_OPTIONS="halt_on_error=1" environment variable would need to be set, since UBSAN's default behaviour is to print an error message and carry on.

[jdemel]

Got it.

CMake provides -DCMAKE_BUILD_TYPE=ASAN. We just add the options here. The way this cmake file works is not obvious.

I merge this PR now. We can add the CI tests in another PR.