sepolgen-ifgen: allow M4 escaped filenames #97

Job	Run time
build (gcc, 3.12, 3.3)	1m 33s
build (gcc, 3.12, 3.3, test-flags-override)	1m 27s
build (gcc, 3.12, 3.3, test-debug)	1m 21s
build (gcc, 3.12, 3.3, linker-bfd)	1m 33s
build (gcc, 3.12, 3.3, linker-gold)	1m 38s
build (gcc, 3.11, 3.3)	1m 38s
build (gcc, 3.10, 3.3)	1m 42s
build (gcc, 3.9, 3.3)	1m 40s
build (gcc, 3.8, 3.3)	1m 37s
build (gcc, 3.7, 3.3)	1m 45s
build (gcc, pypy3.7, 3.3)	2m 22s
build (gcc, 3.12, 3.2)	1m 39s
build (gcc, 3.12, 3.1)	1m 37s
build (gcc, 3.12, 3.0)	1m 35s
build (gcc, 3.12, 2.7)	1m 49s
build (gcc, 3.12, 2.6)	1m 54s
build (gcc, 3.12, 2.5)	1m 45s
build (clang, 3.12, 3.3)	1m 40s
build (clang, 3.12, 3.3, test-flags-override)	1m 24s
build (clang, 3.12, 3.3, test-debug)	1m 29s
build (clang, 3.11, 3.3)	1m 36s
build (clang, 3.10, 3.3)	1m 48s
build (clang, 3.9, 3.3)	1m 39s
build (clang, 3.8, 3.3)	1m 39s
build (clang, 3.7, 3.3)	1m 43s
build (clang, pypy3.7, 3.3)	1m 58s
build (clang, 3.12, 3.2)	1m 38s
build (clang, 3.12, 3.1)	1m 37s
build (clang, 3.12, 3.0)	1m 39s
build (clang, 3.12, 2.7)	1m 49s
build (clang, 3.12, 2.6)	1m 55s
build (clang, 3.12, 2.5)	1m 49s
build (gcc, 3.12, 3.3, sanitizers)	1m 56s
	55m 54s

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