Fix lround, llround missing exceptions close to overflow threshold (bug 19088).

The dbl-64, ldbl-96 and ldbl-128 implementations of lround and llround
fail to produce "invalid" exceptions in cases where the rounded result
overflows the target type, but truncating the floating-point argument
to the next integer towards zero does not overflow it (so in
particular casts do not produce such exceptions).  (This issue cannot
arise for float, or for double with 64-bit target type, or for ldbl-96
with 64-bit target type and negative arguments, because of
insufficient precision in the floating-point type for arguments with
the relevant property to exist.)

This patch fixes these problems by inserting checks for the special
cases that can occur in each implementation, and explicitly raising
FE_INVALID (and avoiding the cast if it might raise spurious
FE_INEXACT).

Tested for x86_64, x86 and mips64.

	[BZ #19088]
	* sysdeps/ieee754/dbl-64/s_lround.c: Include <fenv.h> and
	<limits.h>.
	(__lround) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_lround.c: Include <fenv.h>
	and <limits.h>.
	(__lround) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-128/s_llroundl.c: Include <fenv.h> and
	<limits.h>.
	(__llroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-128/s_lroundl.c: Include <fenv.h> and
	<limits.h>.
	(__lroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-96/s_llroundl.c: Include <fenv.h> and
	<limits.h>.
	(__llroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-96/s_lroundl.c: Include <fenv.h> and
	<limits.h>.
	(__lroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* math/libm-test.inc (lround_test_data): Add more tests.
	(llround_test_data): Likewise.

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