This function saves the binary content of the compiled file into an already opened file. This is called from both build_SaveCode and from build_SaveECode.
The file fp is not closed even if error occures while writing the file.
int build_SaveCore(pBuildObject pBuild,
The function returns BU_ERROR_SUCCESS (zero) if there was no error or BU_ERROR_FAIL if the function fails
writing the file.