i#3544 RV64: Port stolen-reg test to RISC-V

[ksco]

Partially enables stolen-reg test for RISC-V, with the synchall translation path unsupported. The following modifications/fixes were made:

1. Changed the default stolen-reg from t3 to s11 to be a callee-saved register;
2. Ported stolen-reg.c and stolen-reg.dll.c to support RISC-V;
3. Fixed instr_is_mov_constant() and instr_is_nop() for the pattern matching in stolen-reg.dll.c to work;
4. Fixed READ_TLS_SLOT() macro register allocation issue;
5. Added more necessary loads/restores for tp register alongside stolen register;
6. Removed duplicated tests in RUNS_ON_QEMU label;

With this patch, the stolen-reg test is now working on real hardware (without the synchall translation path), but like many other tests related to signals, it does not work on QEMU.