Update VERSIONs to 3.7-rc3 for release. #20

Job	Run time
build (gcc, 3.12, 3.3)	1m 34s
build (gcc, 3.12, 3.3, test-flags-override)	1m 20s
build (gcc, 3.12, 3.3, test-debug)	1m 22s
build (gcc, 3.12, 3.3, linker-bfd)	1m 56s
build (gcc, 3.12, 3.3, linker-gold)	1m 36s
build (gcc, 3.11, 3.3)	1m 27s
build (gcc, 3.10, 3.3)	1m 48s
build (gcc, 3.9, 3.3)	1m 52s
build (gcc, 3.8, 3.3)	2m 6s
build (gcc, 3.7, 3.3)	1m 46s
build (gcc, pypy3.7, 3.3)	2m 1s
build (gcc, 3.12, 3.2)	1m 46s
build (gcc, 3.12, 3.1)	2m 19s
build (gcc, 3.12, 3.0)	1m 39s
build (gcc, 3.12, 2.7)	1m 46s
build (gcc, 3.12, 2.6)	1m 42s
build (gcc, 3.12, 2.5)	1m 43s
build (clang, 3.12, 3.3)	1m 50s
build (clang, 3.12, 3.3, test-flags-override)	1m 34s
build (clang, 3.12, 3.3, test-debug)	1m 26s
build (clang, 3.11, 3.3)	1m 57s
build (clang, 3.10, 3.3)	1m 51s
build (clang, 3.9, 3.3)	1m 47s
build (clang, 3.8, 3.3)	1m 52s
build (clang, 3.7, 3.3)	1m 46s
build (clang, pypy3.7, 3.3)	2m 8s
build (clang, 3.12, 3.2)	2m 16s
build (clang, 3.12, 3.1)	1m 38s
build (clang, 3.12, 3.0)	1m 36s
build (clang, 3.12, 2.7)	1m 58s
build (clang, 3.12, 2.6)	2m 10s
build (clang, 3.12, 2.5)	1m 55s
build (gcc, 3.12, 3.3, sanitizers)	2m 11s
	59m 38s

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