added -Wshadow to the list of compiler args and fixed issues that it pointed out

meson.build

src/batchmode/batchmode_loop.c

src/binary_c_code_options.h

src/binary_c_debug.h

src/binary_c_function_macros.h

src/binary_c_maths.h

src/binary_c_structures.h

src/common_envelope/common_envelope_evolution_BSE.c

src/control/check_stopfile.c

src/disc/disc_make_derived_power_laws.c

src/disc/disc_monotonic_check.c

src/disc/disc_photoevaporation.c

src/ensemble/ensemble_detect_new_PN.c

src/ensemble/ensemble_log.c

src/ensemble/ensemble_macros.h

src/ensemble/ensemble_planetary_nebulae.c

src/ensemble/ensemble_prototypes.h

src/evolution/evolution_rejection_same_tests.c

src/evolution/evolution_rejection_shorten_tests.c

src/evolution/evolution_time_zero_setup.c