[PPC] Fix bootstrap for non-SVR4 targets.

[PPC] Fix bootstrap for non-SVR4 targets.

The recent change to move code into the new rs6000-call.c file is missing a
default value for the TARGET_NO_PROTOTYPE value (which only affects targets
that don’t include svr4.h).  Fixed by moving the fallback setting from
rs6000.c (which has no uses now) to rs6000-call.c.

2019-07-21  Iain Sandoe  <iain@sandoe.co.uk>

	* config/rs6000/rs6000.c (TARGET_NO_PROTOTYPE): Move from here...
	* config/rs6000/rs6000-call.c: ... to here.

From-SVN: r273646