JIT

Allow overriding COMPILER with UNVERSIONED_COMPILER #55

Job	Run time
aarch64-unknown-linux-gnu/gcc (Debug)	9m 12s
JIT without optimizations (Debug)	3m 49s
aarch64-unknown-linux-gnu/gcc (Release)	6m 41s
Free-Threaded (Debug)	4m 22s
Interpreter (Debug)	13m 1s
x86_64-pc-windows-msvc/msvc (Debug)	30m 1s
x86_64-unknown-linux-gnu/gcc (Debug)	15m 10s
x86_64-apple-darwin/clang (Debug)	38m 39s
x86_64-apple-darwin/clang (Release)	27m 57s
JIT with tail calling interpreter	4m 58s
i686-pc-windows-msvc/msvc (Release)	16m 21s
x86_64-unknown-linux-gnu/gcc (Release)	8m 54s
i686-pc-windows-msvc/msvc (Debug)	22m 26s
aarch64-apple-darwin/clang (Release)	16m 58s
aarch64-apple-darwin/clang (Debug)	16m 1s
aarch64-pc-windows-msvc/msvc (Debug)	25m 41s
aarch64-pc-windows-msvc/msvc (Release)	20m 41s
x86_64-pc-windows-msvc/msvc (Release)	15m 50s
	4h 56m 42s

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