Clarify define_insn documentation

[Jeff Law]

On 06/06/2017 12:55 PM, Richard Sandiford wrote:
> This patch tries to clarify some of the restrictions on define_insn
> conditions, and also on the use of "#".
> 
> OK to install?
> 
> Richard
> 
> 
> 2017-06-06  Richard Sandiford  <richard.sandiford@linaro.org>
> 
> gcc/
> 	* doc/md.texi: Clarify the restrictions on a define_insn condition.
> 	Say that # requires an associated define_split to exist, and that
> 	the define_split must be suitable for use after register allocation.
OK.
jeff