Cleanup trailing whitespaces and indentation that uses spaces before tabs

Correct spacing to fix warnings reported by
git diff --check 4b825dc642cb6eb9a060e54bf8d69288fbee4904 HEAD

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
diff --git a/test/childthread.c b/test/childthread.c
index c580db2..e89fb14 100644
--- a/test/childthread.c
+++ b/test/childthread.c
@@ -1,7 +1,7 @@
 /* Test exit of a child of a TCB_EXITING child where the toplevel process starts
  * waiting on it.  The middle one gets detached and strace must update the
  * toplevel process'es number of attached children to 0.
- * 
+ *
  * gcc -o test/childthread test/childthread.c -Wall -ggdb2 -pthread;./strace -f ./test/childthread
  * It must print: write(1, "OK\n", ...
  */