Add CIRGen and LowerToLLVM support for remaining pointer arithmetic extensions for C

[bcardosolopes]

From clang/test/CIR/CodeGen/pointer-arith-ext.c:

...

// FIXME: add support for the remaining ones.
// FP f5(FP a, int b) { return a + b; }
// FP f5_1(FP a, int b) { return (a += b); }
// FP f6(int a, FP b) { return a + b; }
// FP f6_1(int a, FP b) { return (a += b); }
// FP f7(FP a, int b) { return a - b; }
// FP f7_1(FP a, int b) { return (a -= b); }
// void f8(void *a, int b) { return *(a + b); }
// void f8_1(void *a, int b) { return a[b]; }

These are really good first issues to tackle.

[PragmaTwice]

Hello, I am new to Clang IR and would like to work on this task. Could you assign it to me if it is still available? Thank you!

[bcardosolopes]

Hi, welcome. These indeed are good ones. Assigned!