testsuite part 2 for _BitInt support [PR102989]

This is second part of the testcase additions in order to fit into
mailing lists limits.  Most of these tests are for the floating
point conversions, atomics, __builtin_*_overflow and -fsanitize=undefined.

2023-09-06  Jakub Jelinek  <jakub@redhat.com>

	PR c/102989
gcc/testsuite/
	* gcc.dg/torture/bitint-20.c: New test.
	* gcc.dg/torture/bitint-21.c: New test.
	* gcc.dg/torture/bitint-22.c: New test.
	* gcc.dg/torture/bitint-23.c: New test.
	* gcc.dg/torture/bitint-24.c: New test.
	* gcc.dg/torture/bitint-25.c: New test.
	* gcc.dg/torture/bitint-26.c: New test.
	* gcc.dg/torture/bitint-27.c: New test.
	* gcc.dg/torture/bitint-28.c: New test.
	* gcc.dg/torture/bitint-29.c: New test.
	* gcc.dg/torture/bitint-30.c: New test.
	* gcc.dg/torture/bitint-31.c: New test.
	* gcc.dg/torture/bitint-32.c: New test.
	* gcc.dg/torture/bitint-33.c: New test.
	* gcc.dg/torture/bitint-34.c: New test.
	* gcc.dg/torture/bitint-35.c: New test.
	* gcc.dg/torture/bitint-36.c: New test.
	* gcc.dg/torture/bitint-37.c: New test.
	* gcc.dg/torture/bitint-38.c: New test.
	* gcc.dg/torture/bitint-39.c: New test.
	* gcc.dg/torture/bitint-40.c: New test.
	* gcc.dg/torture/bitint-41.c: New test.
	* gcc.dg/torture/bitint-42.c: New test.
	* gcc.dg/atomic/stdatomic-bitint-1.c: New test.
	* gcc.dg/atomic/stdatomic-bitint-2.c: New test.
	* gcc.dg/dfp/bitint-1.c: New test.
	* gcc.dg/dfp/bitint-2.c: New test.
	* gcc.dg/dfp/bitint-3.c: New test.
	* gcc.dg/dfp/bitint-4.c: New test.
	* gcc.dg/dfp/bitint-5.c: New test.
	* gcc.dg/dfp/bitint-6.c: New test.
	* gcc.dg/ubsan/bitint-1.c: New test.
	* gcc.dg/ubsan/bitint-2.c: New test.
	* gcc.dg/ubsan/bitint-3.c: New test.