Update VERSIONs to 3.6-rc1 for release. #523

Job	Run time
build (gcc, 3.11, 3.1)	2m 35s
build (gcc, 3.11, 3.1, test-flags-override)	2m 10s
build (gcc, 3.11, 3.1, test-debug)	2m 6s
build (gcc, 3.11, 3.1, linker-bfd)	1m 32s
build (gcc, 3.11, 3.1, linker-gold)	2m 21s
build (gcc, 3.10, 3.1)	2m 20s
build (gcc, 3.9, 3.1)	3m 10s
build (gcc, 3.8, 3.1)	2m 49s
build (gcc, 3.7, 3.1)	1m 35s
build (gcc, pypy3.7, 3.1)	2m 0s
build (gcc, 3.11, 3.0)	2m 9s
build (gcc, 3.11, 2.7)	2m 24s
build (gcc, 3.11, 2.6)	1m 53s
build (gcc, 3.11, 2.5)	1m 50s
build (clang, 3.11, 3.1)	1m 35s
build (clang, 3.11, 3.1, test-flags-override)	1m 56s
build (clang, 3.11, 3.1, test-debug)	2m 35s
build (clang, 3.10, 3.1)	3m 6s
build (clang, 3.9, 3.1)	2m 9s
build (clang, 3.8, 3.1)	2m 46s
build (clang, 3.7, 3.1)	2m 28s
build (clang, pypy3.7, 3.1)	2m 43s
build (clang, 3.11, 3.0)	1m 34s
build (clang, 3.11, 2.7)	1m 47s
build (clang, 3.11, 2.6)	1m 51s
build (clang, 3.11, 2.5)	2m 21s
build (gcc, 3.11, 3.1, sanitizers)	1m 55s
	59m 40s

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