请教一个关于makefile的问题

这可以解释你看到的:
The program used as the shell is taken from the variable SHELL. If this
variable is not set in your makefile, the program /bin/sh is used as the shell.

另外，我试了一下，用make 3.80和3.81/3.82的结果不一样，你可以试一下。