Improve coverage branches tests #1018

Job	Run time
Docker	8m 36s
Coverage (STP)	37m 22s
macOS	7m 9s
clang-format	6m 44s
Coverage (Z3)	37m 38s
Linux (LLVM 14)	10m 54s
Linux (LLVM 13)	12m 35s
Linux (LLVM 12)	10m 54s
Linux (LLVM 11, Doxygen)	10m 54s
Linux (LLVM 10)	10m 54s
Linux (LLVM 9)	10m 53s
Linux (ASan)	10m 56s
Linux (UBSan)	12m 19s
Linux (MSan)	10m 58s
Linux (Z3 only)	10m 54s
Linux (metaSMT)	10m 56s
Linux (STP master)	10m 22s
Linux (Latest klee-uclibc)	11m 3s
Linux (Asserts disabled)	10m 53s
Linux (No TCMalloc, optimised runtime)	10m 54s
	4h 23m 48s

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