lib/, src/: Use _Generic(3) instead of __builtin_types_compatible_p()

[alejandro-colomar]

_Generic(3) is standard C since ISO C11, so let's avoid unnecessarily using this GNU C extension.

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Revisions:

v1b

• Rebase

$ git rd 
1:  ab202253b = 1:  39263c9e1 lib/typetraits.h: is_same_typeof(): Remove unused macro
2:  868a522ff = 2:  44a9d50a5 lib/, src/: Use _Generic(3) instead of __builtin_types_compatible_p()

v1c

• Rebase

$ git rd 
1:  39263c9e1 = 1:  d05c9337d lib/typetraits.h: is_same_typeof(): Remove unused macro
2:  44a9d50a5 = 2:  3351d3d4a lib/, src/: Use _Generic(3) instead of __builtin_types_compatible_p()