[Ptests] adds PLUGIN macro and the PLUGIN directive sets the macro

ptests/ptests.ml

src/plugins/report/tests/report/classify.c

src/plugins/report/tests/report/csv.c

src/plugins/report/tests/report/test_config

tests/builtins/big_local_array.i

tests/builtins/test_config

tests/constant_propagation/bts117.c

tests/constant_propagation/test_config

tests/impact/test_config

tests/journal/control2.c

tests/journal/intra.i

tests/libc/coverage.c

tests/libc/fc_libc.c

tests/metrics/test_config

tests/misc/add_assigns.i

tests/misc/bts1347.i

tests/misc/obfuscate.c

tests/occurrence/test_config

tests/pdg/bts1194.c

tests/pdg/test_config