Actually run goto-cc-multi-file regression suite

We had this folder in place for a while, but it was neither included
in the Makefile nor the CMake-based regression test execution.

Author: tautschnig

Diff for: regression/CMakeLists.txt

@@ -77,6 +77,7 @@ add_subdirectory(k-induction)
 add_subdirectory(goto-harness)
 add_subdirectory(goto-harness-multi-file-project)
 add_subdirectory(goto-cc-file-local)
+add_subdirectory(goto-cc-multi-file)
 add_subdirectory(goto-cc-regression-gh-issue-5380)
 add_subdirectory(linking-goto-binaries)
 add_subdirectory(symtab2gb)

Diff for: regression/Makefile

@@ -50,6 +50,7 @@ DIRS = cbmc-shadow-memory \
        goto-harness \
        goto-harness-multi-file-project \
        goto-cc-file-local \
+       goto-cc-multi-file \
        goto-cc-regression-gh-issue-5380 \
        linking-goto-binaries \
        symtab2gb \