Merge pull request github#18537 from jketema/elifdef

C++: Support `#elifdef`, `#elifndef`, and MSVC's `#import`

Author: jketema

cpp/downgrades/59cb96ca699929b63941e81905f9b8de7eed59a6/old.dbscheme

@@ -0,0 +1,21 @@
+class PreprocessorDirective extends @preprocdirect {
+  string toString() { none() }
+}
+
+class Location extends @location_default {
+  string toString() { none() }
+}
+
+bindingset[kind]
+int getKind(int kind) {
+  if kind = 14
+  then result = 6 // Represent MSFT #import as #include
+  else
+    if kind = 15 or kind = 6
+    then result = 3 // Represent #elifdef and #elifndef as #elif
+    else result = kind
+}
+
+from PreprocessorDirective ppd, int kind, Location l
+where preprocdirects(ppd, kind, l)
+select ppd, getKind(kind), l