I am seeing this same issue using the Raspberry Pi toolchain:
1>C:\BitBucket\ftk\src\ftk.c(96): error VGDB1001: multiple definition of `ftk_deinit'
1> Debug/ftk.o:C:\BitBucket\ftk/src/ftk.c:96: first defined here
1> Debug/ftk.o: In function `ftk_init':
1> ftk.c:(.text.ftk_init+0x0): multiple definition of `ftk_init'
Please check your link command line in the build output. Does it include the ftk.o file twice? If yes, please ensure that you don’t have two different ftk.c files in your project.