backport: re PR tree-optimization/88074 (g++ hangs on math expression)

backport: re PR tree-optimization/88074 (g++ hangs on math expression)

	Backported from mainline
	2019-02-20  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/88074
	PR middle-end/89415
	* toplev.c (do_compile): Double the emin/emax exponents to workaround
	buggy mpc_norm.

	* gcc.dg/pr88074-2.c: New test.

	2019-02-19  Richard Biener  <rguenther@suse.de>

        PR middle-end/88074
	* toplev.c (do_compile): Initialize mpfr's exponent range
	based on available float modes.

	* gcc.dg/pr88074.c: New testcase.

From-SVN: r270712