Tab as the prefix for command lines is a property of all Makefile formats I'm aware of (though not of many other build script formats). Make itself (including GNU Make) does not generally use M4, though both Autoconf and Automake use it, often in conjunction with Make, as part of the Autotools suite which is also published by GNU.

So, none of the above, in itself. It is a historical anomaly which has been preserved.