ld: Add the entry symbol, _main, for LynxOS targets

ld: Add the entry symbol, _main, for LynxOS targets

Add the entry symbol, _main, to fix:

FAIL: ld-elf/64ksec
FAIL: ld-elf/comm-data4
FAIL: ld-elf/comm-data5
FAIL: ld-elf/eh5
FAIL: ld-elf/empty
FAIL: ld-elf/empty2
FAIL: ld-elf/endsym
FAIL: ld-elf/exclude3a
FAIL: ld-elf/linkonce2
FAIL: ld-elf/orphan3
FAIL: ld-elf/pr12851
FAIL: ld-elf/pr14156a
FAIL: ld-elf/pr14156b
FAIL: ld-elf/pr14926
FAIL: ld-elf/pr20513a
FAIL: ld-elf/pr20513b
FAIL: ld-elf/stab
FAIL: ld-elf/var1
FAIL: ld-elf/warn3
FAIL: section size overflow

for i386-lynxos target.

	* testsuite/ld-checks/over2.s: Add "_main" for LynxOS targets.
	* testsuite/ld-elf/comm-data4.s: Likewise.
	* testsuite/ld-elf/comm-data5.s: Likewise.
	* testsuite/ld-elf/eh5b.s: Likewise.
	* testsuite/ld-elf/empty.s: Likewise.
	* testsuite/ld-elf/empty2.s: Likewise.
	* testsuite/ld-elf/exclude3.s: Likewise.
	* testsuite/ld-elf/fini0.s: Likewise.
	* testsuite/ld-elf/init0.s: Likewise.
	* testsuite/ld-elf/linkonce1b.s: Likewise.
	* testsuite/ld-elf/orphan3a.s: Likewise.
	* testsuite/ld-elf/pr14926.s: Likewise.
	* testsuite/ld-elf/pr20513a.s: Likewise.
	* testsuite/ld-elf/sec64k.exp: Likewise.
	* testsuite/ld-elf/start.s: Likewise.
	* testsuite/ld-elf/var1.s: Likewise.