Improve coverage branches tests #1022

Job	Run time
clang-format	6m 47s
Coverage (STP)	18m 57s
Linux (LLVM 14)	10m 59s
Coverage (Z3)	18m 58s
macOS	10m 18s
Linux (LLVM 13)	11m 1s
Docker	8m 31s
Linux (LLVM 12)	10m 41s
Linux (LLVM 11, Doxygen)	11m 3s
Linux (LLVM 10)	11m 1s
Linux (LLVM 9)	11m 1s
Linux (ASan)	11m 3s
Linux (UBSan)	11m 0s
Linux (MSan)	11m 3s
Linux (Z3 only)	10m 19s
Linux (metaSMT)	10m 49s
Linux (STP master)	10m 59s
Linux (Latest klee-uclibc)	11m 1s
Linux (Asserts disabled)	11m 1s
Linux (No TCMalloc, optimised runtime)	11m 0s
	3h 47m 32s

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