They contain things like -fvisibility=hidden which, in case of building with
CFLAGS="-flto -O2" LDFLAGS="-Wl,--as-needed -flto", results in the linker
throwing out unused symbols and not linking the dumper against libregress.

This results in errors like:
  Invalid GType function: 'regress_test_enum_get_type'
  Failed to find symbol 'regress_test_enum_get_type'

Fix this by only passing the required CFLAGS to the scanner instead.