* lib/gdb.exp (gdb_skip_float_test): New proc. Skip test if
no floating point support.
(gdb_skip_stdio_test): New proc. Skip test if no stdio support.
* gdb.base/call-ar-st.exp: Use above procs to skip tests.
* gdb.base/call-rt-st.exp: Ditto.
* gdb.base/call-strs.exp: Ditto.
* gdb.base/sizeof.exp (check_sizeof): Skip if no printf support.
* gdb.base/varargs.exp: Skip entire test if no printf support.
* gdb.base/ending-run.exp (Step to return): Skip if no printf supt.
* gdb.base/shlib-call.exp: Skip several tests if no printf support.
