merge GCC 10.4 into gcc.old.

merge GCC 9.3 into gcc.old.

merge GCC 8.4 into gcc.old.

merge gcc 7.4 into gcc.old part 2.

attempt to fix liblto_plugin build. on sparc it at least now
appears to have no missing symbols. add xasprintf.c, xvasprintf.c,
and vprintf-support.c.

fix vprintf-support.c to include vprintf-supp

attempt to fix liblto_plugin build. on sparc it at least now
appears to have no missing symbols. add xasprintf.c, xvasprintf.c,
and vprintf-support.c.

fix vprintf-support.c to include vprintf-support.h.

show more ...

import the GCC 5.4 srcs from -current as gcc.old in preparation for GCC 6.