Fix missing main() in libbenchmark_main.a again
In the previous version #968461, replaced by -ffat-lto-objects is a insufficient fix because it disables LTO itself unexpectedly ( -ffat-lto-objects should be used with -flto)
Instead, excluding libbenchmark_main.a from dh_strip may be a better solution without stripping LTO information. [1]
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=939656 dh_strip should strip sections with LTO information from .a and .o files