x86: Insert ENDBR if function will be called indirectly

x86: Insert ENDBR if function will be called indirectly

Since constant_call_address_operand has

;; Test for a pc-relative call operand
(define_predicate "constant_call_address_operand"
  (match_code "symbol_ref")
{
  if (ix86_cmodel == CM_LARGE || ix86_cmodel == CM_LARGE_PIC
      || flag_force_indirect_call)
    return false;
  if (TARGET_DLLIMPORT_DECL_ATTRIBUTES && SYMBOL_REF_DLLIMPORT_P (op))
    return false;
  return true;
})

even if cgraph_node::get (cfun->decl)->only_called_directly_p () returns
false, the fuction may still be called indirectly.  Copy the logic from
constant_call_address_operand to rest_of_insert_endbranch to insert ENDBR
at function entry if function will be called indirectly.

NB: gcc.target/i386/pr94417-2.c is updated to expect 4 ENDBRs, instead
of 2, since only GCC 10 has the fix for PR target/89355 not to insert
ENDBR after NOTE_INSN_DELETED_LABEL.

gcc/

	Backport from master
	PR target/94417
	* config/i386/i386.c (rest_of_insert_endbranch): Insert ENDBR at
	function entry if function will be called indirectly.

gcc/testsuite/

	Backport from master
	PR target/94417
	* gcc.target/i386/pr94417-1.c: New test.
	* gcc.target/i386/pr94417-2.c: Likewise.
	* gcc.target/i386/pr94417-3.c: Likewise.

(cherry picked from commit c5f379653964a1d2c7037b2de3e947a48370a198)