[tests] add test for JCDB subdir

tests/jcdb/oracle/subdir.res

+[kernel] Parsing PWD/../subdir.c (with preprocessing)

tests/jcdb/subdir.c

+/* run.config
+   NOFRAMAC:
+   EXECNOW: LOG subdir.res LOG subdir.err (cd @PTEST_DIR@/subdir1 && @frama-c@ -add-symbolic-path $PWD/..:PWD/.. -json-compilation-database ../subdir.json ../subdir.c) > @PTEST_RESULT@/subdir.res 2> @PTEST_RESULT@/subdir.err
+*/
+
+// this test must be run with PWD in subdir1
+#include "subdir1/header.h"
+#include "included.h" // in subdir2, via '-Isubdir2' in subdir.json
+#include "__fc_builtin.h" // to check that Frama-C's libc is correctly included
+
+int main() {
+  return ONE + TWO;
+}

tests/jcdb/subdir.json

+[
+    { "directory": ".",
+      "command": "g++ -Isubdir2",
+      "file": "subdir.c"
+    }
+]

tests/jcdb/subdir1/header.h

+#define ONE 1

tests/jcdb/subdir2/included.h

+// to be included by subdir.c
+
+#define TWO 2