Allow makefile variables use command line/env

Map-A-Droid / MAD-docs

Documentation for Map-A-Droid

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Allow makefile variables use command line/env #54

Closed reedy closed 4 years ago

reedy commented 4 years ago

Fixes https://github.com/Map-A-Droid/MAD-docs/issues/53

As per https://www.gnu.org/software/make/manual/make.html#Flavors

There is another assignment operator for variables, ‘?=’. This is called a conditional variable assignment operator, because it only has an effect if the variable is not yet defined.

reedy commented 4 years ago

In favour of https://github.com/Map-A-Droid/MAD-docs/pull/58