Accessing the initializer of a static constexpr in LLVM C++17 - clang

Question

In an LLVM-9.x plugin, I'd like to access the initializer (= 42) associated with variable Y in the template specialization T<42> foo:
template<int X>
class T {
//Clang produces different ASTs on this code in C++14 and C++17
//(in 17, there's no initializer for Y (= 42) in the specialized
//class foo below).
static constexpr int Y = X;
};
T<42> foo;
With clang++ -std=c++14 I get an AST (excerpted) that looks like:
> clang++ -std=c++14 -Xclang -ast-dump -fsyntax-only file.cpp
|-ClassTemplateDecl 0x563e38c10980 <test_constexpr.cpp:1:1, line:7:1> line:2:7 T
...
| | `-VarDecl 0x563e38c10c98 <line:6:3, col:28> col:24 Y 'const int' static constexpr cinit
| | `-DeclRefExpr 0x563e38c10d00 <col:28> 'int' NonTypeTemplateParm 0x563e38c10878 'X' 'int'
| `-ClassTemplateSpecializationDecl 0x563e38c10d78 <line:1:1, line:7:1> line:2:7 class T
...
| |-VarDecl 0x563e38c110c8 <line:6:3, col:28> col:24 Y 'const int' static constexpr cinit
| | `-SubstNonTypeTemplateParmExpr 0x563e38c11160 <col:28> 'int' <== MISSING in C++17 BELOW
| | `-IntegerLiteral 0x563e38c11140 <col:28> 'int' 42 <== MISSING in C++17 BELOW
and things work fine (assuming decl is the second VarDecl for Y, I'm able to access 42 by decl->getInit()).
With clang++ -std=c++17, however, I get the new AST:
> clang++ -std=c++17 -Xclang -ast-dump -fsyntax-only file.cpp
|-ClassTemplateDecl 0x56114838ff40 <test_constexpr.cpp:1:1, line:7:1> line:2:7 T
...
| | `-VarDecl 0x561148390258 <line:6:3, col:28> col:24 Y 'const int' static inline constexpr cinit
| | `-DeclRefExpr 0x5611483902c0 <col:28> 'int' NonTypeTemplateParm 0x56114838fe38 'X' 'int'
| `-ClassTemplateSpecializationDecl 0x561148390338 <line:1:1, line:7:1> line:2:7 class T
...
| |-VarDecl 0x561148390688 <line:6:3, col:24> col:24 Y 'const int' static constexpr
in which the initializing expression for Y (-IntegerLiteral 0x563e38c11140 <col:28> 'int' 42) no longer appears. Including a use of Y like int z = Y in the class definition causes the initializer to reappear.
Questions
Should I expect not to see the initializer expression in the AST above in clang++ -std=c++17?
If so, what's the best way to access the initializer for Y in T<42> foo from within an LLVM-9.x plugin?
Thanks! And please let me know if I've left out relevant information -- I'll be happy to update the question to provide it.