orc: Fix warning because of a mismatched OrcExecutor function signature
Fixes warning C4113 in MSVC:
testsuite/orcc/testorc.c(27292): warning C4113: 'void (__cdecl *)(OrcExecutor *restrict )' differs in parameter lists from 'OrcExecutorFunc'
The ORC_RESTRICT definition was extracted from orcprogram-c.c.