c-family: Fix ICE on __builtin_speculation_safe_value () [PR94755]

c-family: Fix ICE on __builtin_speculation_safe_value () [PR94755]

When this builtin has no parameters, speculation_safe_value_resolve_call
returns BUILT_IN_NONE, but resolve_overloaded_builtin uselessly
dereferences the first param just to return error_mark_node immediately.

The following patch rearranges it so that we only read the first parameter
if fncode is not BUILT_IN_NONE.

2020-04-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/94755
	* c-common.c (resolve_overloaded_builtin): Return error_mark_node for
	fncode == BUILT_IN_NONE before initialization of first_param.

	* c-c++-common/pr94755.c: New test.