C++: Add test for mixed implicit/explicit function declarations

Author: calumgrant

cpp/ql/test/library-tests/exprs/implicitly_declared/functions.expected

@@ -0,0 +1,6 @@
+| implicit2.c:1:7:1:7 | g | file://:0:0:0:0 | float |
+| implicit2.c:1:7:1:7 | g | file://:0:0:0:0 | int |
+| implicit.c:1:6:1:6 | f | file://:0:0:0:0 | void |
+| implicit.c:3:5:3:5 | g | file://:0:0:0:0 | float |
+| implicit.c:3:5:3:5 | g | file://:0:0:0:0 | int |
+| implicit.cpp:3:6:3:6 | f | file://:0:0:0:0 | void |

cpp/ql/test/library-tests/exprs/implicitly_declared/functions.ql

@@ -0,0 +1,5 @@
+import cpp
+
+from Function fn
+where fn.fromSource()
+select fn, fn.getType()

cpp/ql/test/library-tests/exprs/implicitly_declared/implicit2.c

@@ -0,0 +1 @@
+float g();