Fix Issue 18493 - [betterC] Can't use aggregated type with postblit

src/core/stdc/stdlib.d

@@ -29,10 +29,14 @@ else version (WatchOS)
 extern (C):
 @system:
 
-/* Placed outside @nogc in order to not constrain what the callback does.
+/* Placed outside `nothrow` and `@nogc` in order to not constrain what the callback does.
  */
 ///
-alias int function(const void*, const void*) _compare_fp_t;
+alias _compare_fp_t = int function(const void*, const void*);
+
+nothrow:
+@nogc:
+
 ///
 inout(void)* bsearch(const void* key, inout(void)* base, size_t nmemb, size_t size, _compare_fp_t compar);
 ///
@@ -51,9 +55,6 @@ void    qsort(void* base, size_t nmemb, size_t size, _compare_fp_t compar);
     bsearch(&key, arr.ptr, arr[0].sizeof, arr.length, &S.cmp);
 }
 
-nothrow:
-@nogc:
-
 ///
 struct div_t
 {

src/rt/profilegc.d

@@ -113,7 +113,7 @@ shared static ~this()
         Entry entry;
 
         // qsort() comparator to sort by count field
-        extern (C) static int qsort_cmp(scope const void *r1, scope const void *r2)
+        extern (C) static int qsort_cmp(scope const void *r1, scope const void *r2) @nogc nothrow
         {
             auto result1 = cast(Result*)r1;
             auto result2 = cast(Result*)r2;

src/rt/trace.d

@@ -156,7 +156,7 @@ private void stack_free(Stack *s)
 //////////////////////////////////////
 // Qsort() comparison routine for array of pointers to SymPair's.
 
-private int sympair_cmp(scope const void* e1, scope const void* e2)
+private int sympair_cmp(scope const void* e1, scope const void* e2) nothrow @nogc
 {
     auto count1 = (*cast(SymPair**)e1).count;
     auto count2 = (*cast(SymPair**)e2).count;
@@ -271,7 +271,7 @@ private void trace_array(Symbol*[] psymbols, Symbol *s, ref uint u)
 //////////////////////////////////////
 // Qsort() comparison routine for array of pointers to Symbol's.
 
-private int symbol_cmp(scope const void* e1, scope const void* e2)
+private int symbol_cmp(scope const void* e1, scope const void* e2) nothrow @nogc
 {
     auto ps1 = cast(Symbol **)e1;
     auto ps2 = cast(Symbol **)e2;