Defines starting with `f' in src

• FFLAG_N src/fpp.c:29
• FFLAG_NAN src/fpp.c:30
• FFLAG_Z src/fpp.c:28
• FIRST_AXIS src/sdlgfx.c:1018
• FIRST_BUTTON src/sdlgfx.c:1019
• FLOPPY_DRIVE_HD src/disk.c:37
• FLOPPY_GAP_LEN src/disk.c:41
• FLOPPY_WRITE_LEN src/disk.c:39
• force_z3 src/expansion.c:91
• FS_GO_DOWN src/filesys.c:117
• FS_STARTUP src/filesys.c:116