Improve factor_out_conditional_operation for conversions and constants

In the case of a NOP conversion (precisions of the 2 types are equal),
factoring out the conversion can be done even if int_fits_type_p returns
false and even when the conversion is defined by a statement inside the
conditional. Since it is a NOP conversion there is no zero/sign extending
happening which is why it is ok to be done here; we were trying to prevent
an extra sign/zero extend from being moved away from definition which no-op
conversions are not.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR tree-optimization/104376
	PR tree-optimization/101541
	* tree-ssa-phiopt.cc (factor_out_conditional_operation):
	Allow nop conversions even if it is defined by a statement
	inside the conditional.

gcc/testsuite/ChangeLog:

	PR tree-optimization/101541
	* gcc.dg/tree-ssa/phi-opt-39.c: New test.