Fix #14898: Update simplecpp to 1.8.1 (#8702) #20256

Job	Run time
build_cmake (ubuntu:25.10, true, true)	5m 43s
build_make (ubuntu:25.10)	3m 1s
build_make (ubuntu:24.04)	4m 26s
build_cmake (ubuntu:24.04, true, true)	5m 23s
build_cmake (alpine:3.23, false, false)	4m 32s
build_make (alpine:3.23)	5m 54s
	28m 59s

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