loongarch: Add SLJIT_UPPER_BITS_SIGN_EXTENDED #51

Job	Run time
build-test-on-arm32	1m 55s
build-test-on-armt2	2m 3s
build-test-on-aarch64	1m 37s
build-test-on-loongarch64	1m 56s
build-test-on-riscv32	2m 8s
build-test-on-riscv32-extensions	2m 20s
build-test-on-riscv64	2m 19s
build-test-on-riscv64-extensions	2m 31s
build-test-on-s390x	2m 0s
build-test-on-x64	17s
build-test-on-x86	20s
	19m 26s

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