1.c:2: error 2: Initializer element is not constant
1.c:3: error 2: Initializer element is not constant
1.c:4: error 2: Initializer element is not constant

The compiler says that Initializer is not constant.

error is with following expressions.
Sbit front = P0^0;
sbit back1 = P0^1;
sbit back2 = P0^2;

Please specify compiler you are using.
Try using preprocessor directives

if you are using SDCC freeware compiler then use
#define front P0_0;
#define back1 P0_1;
#define back2 P0_2;

regarding warnings
1.c:16: warning 84: 'auto' variable 'd4' may be used before initialization and so.

you are comparing d4 without initialization ie. d4 doest have known value at the time of comparison.

also C is case sensitive
Sbit and sbit are different.