Let's take a look.
The shell bone script for Come is
which did mean Wheat originally. We can see that it looks like a plant of wheat.
It is a pictography character.
Its big seal script is
The shell bone script for Wheat is
Let's see its big seal script first, which is easier to be understood.
It is an ideogram character.
However, the two characters exchanged the meaning in long history.
來，original meant Wheat, but it means Come
麥，original meant Come, but it means Wheat.
I don't know why this could have happened.
The small seal script for Come is
The clerical script for Come is
The clerical script for wheat is
The current standard printing script for traditional character of Come is
very similar to the clerical script.
The current standard printing script for simplified character of Come is
changed a little bit in the middle, but still similar to its clerical script. However, it has only one stroke less than the traditional script (8 strokes vs 7 strokes), which is really necessary to simplify?
The current standard printing script for traditional character of Wheat is
very similar to clerical script.
The current standard printing script for simplified character of Wheat is
not much similarity left on the top part.
The pinyin for 來 (Come) is Lai2.
The pinyin for 麥 (Wheat) is Mai4.