testsuite: i386: Restrict gcc.target/i386/pr120881-1?.c to Linux

testsuite: i386: Restrict gcc.target/i386/pr120881-1?.c to Linux

Two tests FAIL on Solaris x86:

FAIL: gcc.target/i386/pr120881-1a.c  at line 4 (test for warnings, line )
FAIL: gcc.target/i386/pr120881-1b.c  at line 4 (test for warnings, line )

producing no message contrary to what the tests expect.  The reason is
similar to previous instances: Solaris doesn't support -mfentry.  Like
previous cases, this patch thus restricts them to Linux.

Tested on i386-pc-solaris2.11 and x86_64-pc-linux-gnu.

2025-12-15  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	* gcc.target/i386/pr120881-1a.c: Restrict to Linux.
	* gcc.target/i386/pr120881-1b.c: Likewise.