[libFuzzer] Clean up headers and file formatting of LibFuzzer files.

Reorganize #includes to follow LLVM Coding Standards.
Include some missing headers. Required to use `Printf()`.

Aside from that, this patch contains no functional change.
It is purely a re-organization.

Differential Revision: https://reviews.llvm.org/D27363

llvm-svn: 289560
diff --git a/llvm/lib/Fuzzer/FuzzerUtilPosix.cpp b/llvm/lib/Fuzzer/FuzzerUtilPosix.cpp
index fc058cd..8b484b8 100644
--- a/llvm/lib/Fuzzer/FuzzerUtilPosix.cpp
+++ b/llvm/lib/Fuzzer/FuzzerUtilPosix.cpp
@@ -8,7 +8,6 @@
 //===----------------------------------------------------------------------===//
 // Misc utils implementation using Posix API.
 //===----------------------------------------------------------------------===//
-
 #include "FuzzerDefs.h"
 #if LIBFUZZER_POSIX
 #include "FuzzerIO.h"
@@ -113,5 +112,6 @@
   return memmem(Data, DataLen, Patt, PattLen);
 }
 
-} // namespace fuzzer
+}  // namespace fuzzer
+
 #endif // LIBFUZZER_POSIX