[testsuite] Add missing fenv effective target to fp-int-convert-timode* tests.

[testsuite] Add missing fenv effective target to fp-int-convert-timode* tests.

2019-01-25  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* doc/sourcebuild.texi (Environment attributes): Add fenv and
	fenv_exceptions description.

2019-01-25  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* lib/target-supports.exp (check_effective_target_fenv): New.
	* gcc.dg/torture/fp-int-convert-float128-timode-3.c: Add missing
	fenv effective target.
	* gcc.dg/torture/fp-int-convert-timode-1.c: Likewise.
	* gcc.dg/torture/fp-int-convert-timode-2.c: Likewise.
	* gcc.dg/torture/fp-int-convert-timode-3.c: Likewise.
	* gcc.dg/torture/fp-int-convert-timode-4.c: Likewise.

From-SVN: r268266