create database for cpp projects compiled with ccache failed #72

[2021-07-13 14:21:43] [build-stdout] cc -g -O2 -DHAVE_CONFIG_H -Wall -I. -DVERSION="4.4" -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -DPREFIX="/usr" -c -o md5.o md5.c
[2021-07-13 14:21:43] [build-stdout] ./mksources
[2021-07-13 14:21:43] [build-stdout] cc bftpdutmp.o commands.o commands_admin.o cwd.o dirlist.o list.o login.o logging.o main.o mystring.o options.o md5.o -lcrypt -o bftpd
Finalizing database at /home/user01/result/db-bftpd.
No source code was seen and extracted to /home/user01/result/db-bftpd.
This can occur if the specified build commands failed to compile or process any code.

• Confirm that there is some source code for the specified language in the project.
• For codebases written in Go, JavaScript, TypeScript, and Python, do not specify
  an explicit --command.
• For other languages, the --command must specify a "clean" build which compiles
  all the source code files without reusing existing build artefacts.

$ which cc
/usr/lib64/ccache/cc