Patch implements PROVIDE command. It is often used in scripts I saw.
Description of PROVIDE (taken from https://www.sourceware.org/binutils/docs-2.10/ld_3.html#SEC17):
In some cases, it is desirable for a linker script to define a symbol only if it is referenced and is not defined by any object included in the link. For example, traditional linkers defined the symbol etext'. However, ANSI C requires that the user be able to use etext' as a function name without encountering an error. The PROVIDE keyword may be used to define a symbol, such as `etext', only if it is referenced but not defined. The syntax is PROVIDE(symbol = expression).