Update VERSIONs to 3.7-rc3 for release. #186

Job	Run time
build (gcc, 3.12, 3.3)	1m 55s
build (gcc, 3.12, 3.3, test-flags-override)	1m 28s
build (gcc, 3.12, 3.3, test-debug)	1m 25s
build (gcc, 3.12, 3.3, linker-bfd)	1m 34s
build (gcc, 3.12, 3.3, linker-gold)	1m 38s
build (gcc, 3.11, 3.3)	1m 48s
build (gcc, 3.10, 3.3)	1m 36s
build (gcc, 3.9, 3.3)	1m 32s
build (gcc, 3.8, 3.3)	1m 35s
build (gcc, 3.7, 3.3)	1m 56s
build (gcc, pypy3.7, 3.3)	2m 2s
build (gcc, 3.12, 3.2)	1m 33s
build (gcc, 3.12, 3.1)	1m 34s
build (gcc, 3.12, 3.0)	1m 45s
build (gcc, 3.12, 2.7)	1m 49s
build (gcc, 3.12, 2.6)	1m 42s
build (gcc, 3.12, 2.5)	1m 48s
build (clang, 3.12, 3.3)	1m 56s
build (clang, 3.12, 3.3, test-flags-override)	1m 41s
build (clang, 3.12, 3.3, test-debug)	1m 33s
build (clang, 3.11, 3.3)	1m 48s
build (clang, 3.10, 3.3)	1m 42s
build (clang, 3.9, 3.3)	1m 46s
build (clang, 3.8, 3.3)	1m 56s
build (clang, 3.7, 3.3)	1m 53s
build (clang, pypy3.7, 3.3)	2m 8s
build (clang, 3.12, 3.2)	1m 42s
build (clang, 3.12, 3.1)	1m 41s
build (clang, 3.12, 3.0)	1m 40s
build (clang, 3.12, 2.7)	2m 7s
build (clang, 3.12, 2.6)	1m 56s
build (clang, 3.12, 2.5)	2m 1s
build (gcc, 3.12, 3.3, sanitizers)	2m 6s
	58m 16s

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