Commonize demangle test pieces; allow for running specific tests and test cases; use linker sets to simplify test definition

@@ -54,10 +54,10 @@
 [/opt/util-tests/tests/grep_test]
 [/opt/util-tests/tests/date_test]
 [/opt/util-tests/tests/chown_test]
 
 [/opt/util-tests/tests/demangle]
-tests = ['afl-fast', 'gcc-libstdc++', 'llvm-stdcxxabi']
+tests = ['c++', 'rust']
 
 [/opt/util-tests/tests/ctf]
 pre = precheck
 tests = [ 'ctftest' ]