Add a test for main () in a shared object

Verify that crt1.o can be used with main () in a shared object.

	* elf/Makefile (tests): Add tst-main1.
	(modules-names): Add tst-main1mod.
	($(objpfx)tst-main1): New.
	(CRT-tst-main1): Likewise.
	(LDFLAGS-tst-main1): Likewise.
	(LDLIBS-tst-main1): Likewise.
	(tst-main1mod.so-no-z-defs): Likewise.
	* elf/tst-main1.c: New file.
	* elf/tst-main1mod.c: Likewise.