Fix bug when optimizing string pools of aligned strings.

Fix bug when optimizing string pools of aligned strings.

Tail optimization of string pools (enabled when linker is run with -O2
or greater) should not be done when the section alignment is greater
than the size of the characters in the strings; otherwise, unaligned
strings may result.

gold/
	PR gold/18010
	* stringpool.cc (Stringpool_template): Don't optimize if section
	alignment is greater than sizeof(char).