Fix JIT page protection errors being ignored

[thomasbuilds]

Since #241 moved virtual_memory to C, setPagesRW, setPagesRX and setPagesRWX ignore the result of mprotect/VirtualProtect. On systems that don't allow executable JIT pages, for example with systemd's MemoryDenyWriteExecute=yes (monero-project/monero#10180) or Windows' Arbitrary Code Guard, randomx_alloc_cache and randomx_create_vm succeed and the first dataset initialization or hash crashes, instead of returning NULL as documented.

This returns the pageProtect result from these functions and throws in the JIT compilers when it fails, like the allocMemoryPages check. The secure VM constructor and randomx_alloc_cache make the JIT buffer executable once, so randomx_create_vm and randomx_alloc_cache return NULL on such systems.