testsuite: i386: Restrict gcc.target/i386/pr80569.c to gas

gcc.target/i386/pr80569.c FAILs on Solaris/x86 with the native
assembler:

FAIL: gcc.target/i386/pr80569.c (test for excess errors)

Excess errors:
Assembler: pr80569.c
        "/var/tmp//ccm4_iqb.s", line 2 : Illegal mnemonic
        Near line: "    .code16gcc"
        "/var/tmp//ccm4_iqb.s", line 2 : Syntax error
        Near line: "    .code16gcc"

.code16gcc is a gas extension, so restrict the test to gas.

Tested on i386-pc-solaris2.11 (as and gas) and i686-pc-linux-gnu.

2024-02-01  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	* gcc.target/i386/pr80569.c: Require gas.