Fix for link failures on boxes with non-gnu compiler.


client/Makefile.am:
  Add a dummy C++ file to client suite to make libtool use a C++ linker:
  this lets client suite link when using yaSSL and a non-gcc C++ compiler.
config/ac-macros/yassl.m4:
  HAVE_YASSL conditional is used to add dummy C++ file if configured with yaSSL.
tests/Makefile.am:
  Add a dummy C++ file to tests to make libtool use a C++ linker:
  this lets tests link when using yaSSL and a non-gcc C++ compiler.
vio/Makefile.am:
  Use dummy C++ file if configured with yaSSL only.