GNU make - Conditional Parts of Makefiles
ftp.gnu.org › old-gnu › Manualsconditional-directive text-if-true endif. The text-if-true may be any lines of text, to be considered as part of the makefile if the condition is true. If the condition is false, no text is used instead. The syntax of a complex conditional is as follows: conditional-directive text-if-true else text-if-false endif.
Conditional Syntax (GNU make)
www.gnu.org › software › makeConditionals affect which lines of the makefile make uses. If the condition is true, make reads the lines of the text-if-true as part of the makefile; if the condition is false, make ignores those lines completely. It follows that syntactic units of the makefile, such as rules, may safely be split across the beginning or the end of the conditional.