implement Path::getCurrentExecutablePath for Haiku (#8677) #1030

Job	Run time
build (tsan, -DANALYZE_THREAD=On, false, thread, false, --executor=thread --error-exitcode=0)	17m 30s
build (asan, -DANALYZE_ADDRESS=On, true, process, false)	15m 55s
build (ubsan, -DANALYZE_UNDEFINED=On, true, process, true)	59m 53s
	1h 33m 18s

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