[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/FuzzerExtFunctionsDlsym.cpp b/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsym.cpp
index 65b0458..06bddd5 100644
--- a/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsym.cpp
+++ b/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsym.cpp
@@ -46,5 +46,7 @@
 
 #undef EXT_FUNC
 }
+
 } // namespace fuzzer
+
 #endif // LIBFUZZER_APPLE