1039 - Unknown token in #undef directive.
Description
A token can only be undefined if it was previously defined.
Example
Config:
#undef THING_WHICH_WAS_NOT_DEFINED
Output:
C:\Test\fbuild.bff(1,8): FASTBuild Error #1039 - Unknown token in #undef directive.
#undef THING_WHICH_WAS_NOT_DEFINED
^
\--here
Fix:
#define THING
#undef THING