[Ada] Crash on universal case expression in fixed-point division

[Ada] Crash on universal case expression in fixed-point division

This patch fixes a compiler abort on a case expression whose
alternatives are universal_real constants, when the case expression is
an operand in a multiplication or division whose other operand is of a
fixed-point type.

2019-09-18  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_res.adb (Set_Mixed_Node_Expression): If a conditional
	expression has universal_real alternaitves and the context is
	Universal_Fixed, as when it is an operand in a fixed-point
	multiplication or division, resolve the expression with a
	visible fixed-point type, which must be unique.

gcc/testsuite/

	* gnat.dg/fixedpnt8.adb: New testcase.

From-SVN: r275864