Use new __traits(classInstanceAlignment)

Tackling the druntime part of issue 16508.

Author: kinke

src/core/internal/traits.d

@@ -234,7 +234,7 @@ if (Ts.length > 0)
 template classInstanceAlignment(T)
 if (is(T == class))
 {
-    alias classInstanceAlignment = maxAlignment!(void*, typeof(T.tupleof));
+    enum classInstanceAlignment = __traits(classInstanceAlignment, T);
 }
 
 /// See $(REF hasElaborateMove, std,traits)

src/core/lifetime.d

@@ -200,12 +200,10 @@ Returns: The newly constructed object.
 T emplace(T, Args...)(void[] chunk, auto ref Args args)
     if (is(T == class))
 {
-    import core.internal.traits : maxAlignment;
-
     enum classSize = __traits(classInstanceSize, T);
     assert(chunk.length >= classSize, "chunk size too small.");
 
-    enum alignment = maxAlignment!(void*, typeof(T.tupleof));
+    enum alignment = __traits(classInstanceAlignment, T);
     assert((cast(size_t) chunk.ptr) % alignment == 0, "chunk is not aligned.");
 
     return emplace!T(cast(T)(chunk.ptr), forward!args);
@@ -242,9 +240,7 @@ T emplace(T, Args...)(void[] chunk, auto ref Args args)
         int virtualGetI() { return i; }
     }
 
-    import core.internal.traits : classInstanceAlignment;
-
-    align(classInstanceAlignment!C) byte[__traits(classInstanceSize, C)] buffer;
+    align(__traits(classInstanceAlignment, C)) byte[__traits(classInstanceSize, C)] buffer;
     C c = emplace!C(buffer[], 42);
     assert(c.virtualGetI() == 42);
 }
@@ -290,7 +286,8 @@ T emplace(T, Args...)(void[] chunk, auto ref Args args)
     }
 
     int var = 6;
-    align(__conv_EmplaceTestClass.alignof) ubyte[__traits(classInstanceSize, __conv_EmplaceTestClass)] buf;
+    align(__traits(classInstanceAlignment, __conv_EmplaceTestClass))
+        ubyte[__traits(classInstanceSize, __conv_EmplaceTestClass)] buf;
     auto support = (() @trusted => cast(__conv_EmplaceTestClass)(buf.ptr))();
 
     auto fromRval = emplace!__conv_EmplaceTestClass(support, 1);
@@ -1198,7 +1195,7 @@ pure nothrow @safe /* @nogc */ unittest
     }
     void[] buf;
 
-    static align(A.alignof) byte[__traits(classInstanceSize, A)] sbuf;
+    static align(__traits(classInstanceAlignment, A)) byte[__traits(classInstanceSize, A)] sbuf;
     buf = sbuf[];
     auto a = emplace!A(buf, 55);
     assert(a.x == 55 && a.y == 55);

src/core/thread/osthread.d

@@ -2002,7 +2002,7 @@ extern (C) void thread_init() @nogc
 }
 
 private alias MainThreadStore = void[__traits(classInstanceSize, Thread)];
-package __gshared align(Thread.alignof) MainThreadStore _mainThreadStore;
+package __gshared align(__traits(classInstanceAlignment, Thread)) MainThreadStore _mainThreadStore;
 
 /**
  * Terminates the thread module. No other thread routine may be called

src/core/thread/threadbase.d

@@ -77,9 +77,7 @@ private
 {
     // Handling unaligned mutexes are not supported on all platforms, so we must
     // ensure that the address of all shared data are appropriately aligned.
-    import core.internal.traits : classInstanceAlignment;
-
-    enum mutexAlign = classInstanceAlignment!Mutex;
+    enum mutexAlign = __traits(classInstanceAlignment, Mutex);
     enum mutexClassInstanceSize = __traits(classInstanceSize, Mutex);
 
     alias swapContext = externDFunc!("core.thread.osthread.swapContext", void* function(void*) nothrow @nogc);

test/init_fini/src/custom_gc.d

@@ -26,7 +26,8 @@ nothrow @nogc:
     {
         import core.stdc.string : memcpy;
 
-        __gshared ubyte[__traits(classInstanceSize, MallocGC)] buf;
+        __gshared align(__traits(classInstanceAlignment, MallocGC))
+            ubyte[__traits(classInstanceSize, MallocGC)] buf;
 
         auto init = typeid(MallocGC).initializer();
         assert(init.length == buf.length);