glsl/list: Fix undefined behaviour of foreach_* macros

glsl/list: Fix undefined behaviour of foreach_* macros

These macros produced a lot of errors with ubsan preventing us from
expanding the ubsan coverage on CIs.

C++ spec has such clause:

 "If the prvalue of type "pointer to cv1 B" points to a B that is
  actually a subobject of an object of type D, the resulting pointer
  points to the enclosing object of type D. Otherwise, the result
  of the cast is undefined."

Ubsan error example:

 ../src/compiler/glsl/builtin_functions.cpp:4945:4: runtime error: downcast of address 0x559b926abb50 which does not point to an object of type 'ir_instruction'
 0x559b926abb50: note: object has invalid vptr
  9b 55 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  58 ba 6a 92 9b 55 00 00  01 00 00 00
               ^~~~~~~~~~~~~~~~~~~~~~~
               invalid vptr
     #0 0x559b914dbe1a in call ../src/compiler/glsl/builtin_functions.cpp:4945

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Acked-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4129>