implement Path::getCurrentExecutablePath for Haiku #20217

Job	Run time
build_cmake (alpine:3.23, false, false)	4m 33s
build_make (ubuntu:25.10)	4m 10s
build_make (ubuntu:24.04)	2m 40s
build_cmake (ubuntu:25.10, true, true)	2m 48s
build_make (alpine:3.23)	6m 0s
build_cmake (ubuntu:24.04, true, true)	2m 37s
	22m 48s

Provide feedback