[NFC][libc++] Fixes comment indention.

The output on eel.is has similar oddities, so I expect this was copy
pasted.

Author: mordante

libcxx/include/stdexcept

@@ -17,14 +17,14 @@ namespace std
 {
 
 class logic_error;
-    class domain_error;
-    class invalid_argument;
-    class length_error;
-    class out_of_range;
+class domain_error;
+class invalid_argument;
+class length_error;
+class out_of_range;
 class runtime_error;
-    class range_error;
-    class overflow_error;
-    class underflow_error;
+class range_error;
+class overflow_error;
+class underflow_error;
 
 for each class xxx_error: