Features: Record initializer list support for Intel 14 and above
Features recorded by commit be910f00 for the Intel
compiler left out initializer list support because our test case in
Tests/CompileFeatures/cxx_generalized_initializers.cpp caused an
internal compiler error. It turns out this is because the Intel
compiler asserts the initializer_list constructor signatures to verify
that they match its own <initializer_list> header. It was our dummy
implementation used to test the language feature without any headers
that caused the ICE. Revise it to use a constructor signature accepted
by the Intel compiler.
Fixes: #17829 (closed)