C++: Add VariableDeclarationEntry test to library-tests/variables/global

Author: igfoo

cpp/ql/test/library-tests/variables/global/vardecl.expected

@@ -0,0 +1,6 @@
+| a.c:4:5:4:6 | definition of is | array of {int} | 1 |
+| a.h:2:12:2:13 | declaration of is | array of 4 {int} | 1 |
+| file://:0:0:0:0 | definition of fp_offset | unsigned int | 1 |
+| file://:0:0:0:0 | definition of gp_offset | unsigned int | 1 |
+| file://:0:0:0:0 | definition of overflow_arg_area | pointer to {void} | 1 |
+| file://:0:0:0:0 | definition of reg_save_area | pointer to {void} | 1 |

cpp/ql/test/library-tests/variables/global/vardecl.ql

@@ -0,0 +1,5 @@
+import cpp
+
+from VariableDeclarationEntry vd, Type t
+where t = vd.getType()
+select vd, t.explain(), count(Type u | u = vd.getType())