Clang-format c/cpp files in test directory (#4192)

This clang-formats c/cpp files in test/ directory, and updates
clang-format-diff.sh so that it does not ignore test/ directory anymore.

bigswitch.cpp is excluded from formatting, because there are big
commented-out code blocks, and apparently clang-format messes up
formatting in them. Also to make matters worse, different clang-format
versions do different things on those commented-out code blocks.

1 files changed, 1 insertions, 2 deletions

diff --git a/test/hello_world.c b/test/hello_world.c
index eb47ea813..ce0cca463 100644
--- a/test/hello_world.c
+++ b/test/hello_world.c
@@ -1,7 +1,6 @@
-#include<stdio.h>
+#include <stdio.h>
 
 int main() {
   printf("hello, world!\n");
   return 0;
 }
-