"Keil C51 provides extensions such as bit, sbit, sfr, the memory-space keywords data, xdata, etc, a pointer implementation to cope with the different memory spaces, etc, etc, etc..."

Thats an advantage of the 8051 having 128 bits which can be used as flags"
But when it comes to portabilty this not a big problem , you can either assign a byte for each flag or make a structure or union of bits in a byte to make a flag depending on how tight your memory is.
And remember when you are using a compiler you dont bother yourself with addressing modes, xdata, pdata etc. The good new compiler would do it efficiently.