Reland "[libFuzzer] Support using libc++"

This is needed in case the users of libFuzzer use libc++ in their
code, which the fuzz target (libFuzzer) will be linked against.
When libc++ source is available, we build a private version of it
and link it against libFuzzer which allows using the same static
library against codebases which use both libc++ and libstdc++.

Differential Revision: https://reviews.llvm.org/D37631

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@322755 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/FuzzerLoop.cpp b/FuzzerLoop.cpp
index 5b451ca..7366f69 100644
--- a/FuzzerLoop.cpp
+++ b/FuzzerLoop.cpp
@@ -826,13 +826,15 @@
 
 extern "C" {
 
-size_t LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
+__attribute__((visibility("default"))) size_t
+LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
   assert(fuzzer::F);
   return fuzzer::F->GetMD().DefaultMutate(Data, Size, MaxSize);
 }
 
 // Experimental
-void LLVMFuzzerAnnounceOutput(const uint8_t *Data, size_t Size) {
+__attribute__((visibility("default"))) void
+LLVMFuzzerAnnounceOutput(const uint8_t *Data, size_t Size) {
   assert(fuzzer::F);
   fuzzer::F->AnnounceOutput(Data, Size);
 }