[SPIRV] Let atomic store store pointers (#201251)
SPIRV atomic store permits only integer or floats as per SPIRV spec.
When compiling libc there several places in the code where pointers are
atomically stored causing compilation to break. It can be fixed by using
casting in the libc code but in order to keep the libc code clean it is
preferrable to do it in SPIRV backend. This change will cast pointer
parameters to integers of appropriate size and generate atomic store
instruction that uses integers per SPIRV spec.
