Ignore generated platform C files

.gitignore

@@ -8,10 +8,10 @@ hashindex.c
 chunker.c
 compress.c
 crypto.c
-platform_darwin.c
-platform_freebsd.c
-platform_linux.c
-platform_posix.c
+src/borg/platform/darwin.c
+src/borg/platform/freebsd.c
+src/borg/platform/linux.c
+src/borg/platform/posix.c
 *.egg-info
 *.pyc
 *.pyo