added missing test/cfg/posix.c file

test/cfg/posix.c

@@ -0,0 +1,19 @@
+
+// Test library configuration for posix.cfg
+//
+// Usage:
+// $ cppcheck --check-library --library=posix --enable=information --error-exitcode=1 --inline-suppr cfg/test/posix.c
+// =>
+// No warnings about bad library configuration, unmatched suppressions, etc. exitcode=0
+//
+
+#include <unistd.h>
+
+void f(char *p) {
+    isatty (0);
+    mkdir (p, 0);
+    getcwd (0, 0);
+    // cppcheck-suppress nullPointer
+    readdir (0);
+}
+