Add -fmin-function-alignmnet

-falign-functions is ignored in cold code, since it is an optimization intended to
improve instruction prefetch.  In some case it is necessary to force alignment for
all functions, so this patch adds -fmin-function-alignment for this purpose.

gcc/ChangeLog:

	PR middle-end/88345
	* common.opt: (flimit-function-alignment): Reorder alphabeticaly
	(fmin-function-alignment): New parameter.
	* doc/invoke.texi: (-fmin-function-alignment): Document.
	(-falign-functions,-falign-loops,-falign-labels): Mention that
	aglinments are ignored in cold code.
	* varasm.cc (assemble_start_function): Handle min-function-alignment.