Update VERSIONs to 3.7-rc1 for release. #570

Job	Run time
build (gcc, 3.12, 3.3)	1m 32s
build (gcc, 3.12, 3.3, test-flags-override)	1m 21s
build (gcc, 3.12, 3.3, test-debug)	1m 24s
build (gcc, 3.12, 3.3, linker-bfd)	1m 34s
build (gcc, 3.12, 3.3, linker-gold)	1m 37s
build (gcc, 3.11, 3.3)	1m 30s
build (gcc, 3.10, 3.3)	1m 31s
build (gcc, 3.9, 3.3)	1m 39s
build (gcc, 3.8, 3.3)	1m 44s
build (gcc, 3.7, 3.3)	1m 41s
build (gcc, pypy3.7, 3.3)	1m 59s
build (gcc, 3.12, 3.2)	1m 47s
build (gcc, 3.12, 3.1)	1m 34s
build (gcc, 3.12, 3.0)	1m 34s
build (gcc, 3.12, 2.7)	1m 46s
build (gcc, 3.12, 2.6)	1m 43s
build (gcc, 3.12, 2.5)	1m 43s
build (clang, 3.12, 3.3)	1m 32s
build (clang, 3.12, 3.3, test-flags-override)	1m 25s
build (clang, 3.12, 3.3, test-debug)	1m 29s
build (clang, 3.11, 3.3)	1m 35s
build (clang, 3.10, 3.3)	1m 37s
build (clang, 3.9, 3.3)	1m 40s
build (clang, 3.8, 3.3)	1m 40s
build (clang, 3.7, 3.3)	1m 43s
build (clang, pypy3.7, 3.3)	2m 10s
build (clang, 3.12, 3.2)	1m 49s
build (clang, 3.12, 3.1)	1m 38s
build (clang, 3.12, 3.0)	1m 40s
build (clang, 3.12, 2.7)	1m 52s
build (clang, 3.12, 2.6)	1m 52s
build (clang, 3.12, 2.5)	2m 4s
build (gcc, 3.12, 3.3, sanitizers)	1m 58s
	55m 23s

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