* lib/intprops.h (_GL_HAS_BUILTIN_ADD_OVERFLOW):
Rely on __has_builtin first, since GCC didn’t introduce it until
GCC 9 so we don’t need to special-case GCC first.
(_GL_HAS_BUILTIN_ADD_OVERFLOW, _GL_HAS_BUILTIN_OVERFLOW_P):
Look at __EDG__ rather than __ICC, since icc defines __EDG__ too.
(_GL_HAS_BUILTIN_MUL_OVERFLOW): Define to 1 in Clang 14 and later,
as a bug fix is scheduled for Clang 14.
(_GL_HAS_BUILTIN_OVERFLOW_P): Do not bother to special-case
__clang__, since __has_builtin should do the right thing anyway.