Also disallow global alias of common symbol

Also disallow global alias of common symbol

We can't create alias of common symbol.  Local alias of common symbol has
been disallowed.  But global alias of common symbol is disallowed when the
common symbol is seen first and silently dropped otherwise.  This patch
disallows alias of common symbol in all cases.

gas/

	PR gas/21667
	* read.c (pseudo_set): Update error message for alias of common
	symbol.
	* write.c (write_object_file): Disallow both local and global
	aliases of common symbol.
	* testsuite/gas/elf/common5a.d: New file.
	* testsuite/gas/elf/common5a.l: Likewise.
	* testsuite/gas/elf/common5a.s: Likewise.
	* testsuite/gas/elf/common5b.d: Likewise.
	* testsuite/gas/elf/common5b.l: Likewise.
	* testsuite/gas/elf/common5b.s: Likewise.
	* testsuite/gas/elf/common5c.d: Likewise.
	* testsuite/gas/elf/common5c.s: Likewise.
	* testsuite/gas/elf/common5d.d: Likewise.
	* testsuite/gas/elf/common5d.s: Likewise.
	* testsuite/gas/elf/elf.exp: Run common5a, common5b, common5c
	and common5d.