JIT

Move LLVM_VERSION env var detection to configure #16

Job	Run time
Interpreter (Debug)	10m 0s
i686-pc-windows-msvc/msvc (Debug)	23m 1s
i686-pc-windows-msvc/msvc (Release)	12m 52s
aarch64-pc-windows-msvc/msvc (Release)	16m 47s
x86_64-apple-darwin/clang (Release)	13m 36s
aarch64-pc-windows-msvc/msvc (Debug)	24m 16s
x86_64-pc-windows-msvc/msvc (Debug)	20m 13s
x86_64-unknown-linux-gnu/gcc (Debug)	11m 47s
x86_64-pc-windows-msvc/msvc (Release)	11m 46s
aarch64-apple-darwin/clang (Release)	9m 32s
x86_64-apple-darwin/clang (Debug)	24m 20s
aarch64-unknown-linux-gnu/gcc (Release)	5m 51s
aarch64-apple-darwin/clang (Debug)	12m 13s
aarch64-unknown-linux-gnu/gcc (Debug)	7m 4s
x86_64-unknown-linux-gnu/gcc (Release)	17m 14s
	3h 40m 32s

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