cpp code coverage: Update after toolchain switch

[umaucher]

After switching the toolchain to the score provided one check the needs to get the coverage back to 100% (or we need to clarify where the drop is coming from).

Change is introduced with #159 -> coverage:

Summary coverage rate:
  lines......: 98.3% (2001 of 2036 lines)
  functions..: 99.5% (436 of 438 functions)
  branches...: 34.9% (2687 of 7702 branches)