Various files had been modified to use the predefine, _CPPBUILDER, when compilation needed to be specific for the C++Builder compiler. This is a made up predefine so it was inserted into each project file. There are predefined macros that can be used instead of this made up one. The __BORLANDC__ macro is defined by the compiler already and includes the version number of the compiler.
Therefore, it would be best to switch this out to use the compiler provided macro. It makes utilization of the library more easy so that others don't have to define _CPPBUILDER anywhere.