sepolgen-ifgen: allow M4 escaped filenames #94

Job	Run time
build (gcc, 3.12, 3.3)	1m 30s
build (gcc, 3.12, 3.3, test-flags-override)	1m 26s
build (gcc, 3.12, 3.3, test-debug)	1m 25s
build (gcc, 3.12, 3.3, linker-bfd)	1m 33s
build (gcc, 3.12, 3.3, linker-gold)	1m 41s
build (gcc, 3.11, 3.3)	1m 31s
build (gcc, 3.10, 3.3)	1m 59s
build (gcc, 3.9, 3.3)	1m 40s
build (gcc, 3.8, 3.3)	1m 36s
build (gcc, 3.7, 3.3)	1m 39s
build (gcc, pypy3.7, 3.3)	1m 56s
build (gcc, 3.12, 3.2)	2m 23s
build (gcc, 3.12, 3.1)	1m 32s
build (gcc, 3.12, 3.0)	1m 32s
build (gcc, 3.12, 2.7)	1m 45s
build (gcc, 3.12, 2.6)	1m 46s
build (gcc, 3.12, 2.5)	2m 43s
build (clang, 3.12, 3.3)	1m 42s
build (clang, 3.12, 3.3, test-flags-override)	1m 36s
build (clang, 3.12, 3.3, test-debug)	1m 29s
build (clang, 3.11, 3.3)	1m 34s
build (clang, 3.10, 3.3)	1m 45s
build (clang, 3.9, 3.3)	1m 56s
build (clang, 3.8, 3.3)	2m 21s
build (clang, 3.7, 3.3)	1m 54s
build (clang, pypy3.7, 3.3)	2m 2s
build (clang, 3.12, 3.2)	1m 52s
build (clang, 3.12, 3.1)	1m 50s
build (clang, 3.12, 3.0)	1m 46s
build (clang, 3.12, 2.7)	2m 11s
build (clang, 3.12, 2.6)	3m 3s
build (clang, 3.12, 2.5)	1m 53s
build (gcc, 3.12, 3.3, sanitizers)	2m 7s
	1h 0m 38s

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