Fix #14898: Update simplecpp to 1.8.1 #20255

Job	Run time
build_make (ubuntu:25.10)	3m 41s
build_make (alpine:3.23)	6m 5s
build_cmake (alpine:3.23, false, false)	3m 42s
build_cmake (ubuntu:24.04, true, true)	3m 2s
build_make (ubuntu:24.04)	4m 6s
build_cmake (ubuntu:25.10, true, true)	3m 6s
	23m 42s

Provide feedback