Add -lmygcc to mysql_config output for libs, libs_r, and embedded_libs.

Required when linking against our static libs, if yassl is used, and gcc
used to build library is significantly different from that which is using
the library.


scripts/mysql_config.sh:
  Add -lmygcc to --libs, --libs_r, and --embedded-libs output, if libmygcc.a
  is found in the pkglibdir.
  
  This works around a problem when linking against the static client
  libs which were built with a different GCC than the current compiler.
  In this case, without -lmygcc, several builtin functions (e.g.,
  __pure_virtual, __builtin_delete) are left undefined.  Currently it
  is yassl which pulls in these symbols.
  
  This isn't a problem when linking against shared libraries, or when
  using the same compiler version.
  
  Currently it shows up with libs built on build.mysql.com with gcc 2.95.3,
  when using them on more recent systems.
  
  
  Also strip the -mcpu, -mtune, and -march cflags.  The calling package can
  determine what optimization parameters to choose.