Fix ldbl-128ibm lrintl, lroundl missing "invalid" exceptions (bug 22690).

Fix ldbl-128ibm lrintl, lroundl missing "invalid" exceptions (bug 22690).

The ldbl-128ibm implementations of lrintl and lroundl are missing
"invalid" exceptions for certain overflow cases when compiled with GCC
8.  The cause of this is after-the-fact integer overflow checks that
fail when the compiler optimizes on the basis of integer overflow
being undefined; GCC 8 must be able to detect new cases of
undefinedness here.

Failure: lrint (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_downward (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_towardzero (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_upward (-0x80000001p0): Exception "Invalid operation" not set

Failure: lround (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_downward (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_towardzero (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_upward (-0x80000001p0): Exception "Invalid operation" not set

(Tested that these failures occur before the patch for powerpc
soft-float, but the issue applies in principle for hard-float as well,
whether or not the particular optimizations in fact occur there at
present.)

This patch fixes the bug by ensuring the additions / subtractions in
question cast arguments to unsigned long int, or use 1UL as a constant
argument, so that the arithmetic occurs in an unsigned type with the
result then converted back to a signed type.

Tested for powerpc (soft-float).

	[BZ #22690]
	* sysdeps/ieee754/ldbl-128ibm/s_lrintl.c (__lrintl): Use unsigned
	long int for arguments of possibly overflowing addition or
	subtraction.
	* sysdeps/ieee754/ldbl-128ibm/s_lroundl.c (__lroundl): Likewise.