[lib/Fuzzer] Add SHA1 implementation from public domain.

Summary:
This adds a SHA1 implementation taken from public domain code.
The change is trivial, but as it involves third-party code I'd like
a second pair of eyes before commit.

LibFuzzer can not use SHA1 from openssl because openssl may not be available
and because we may be fuzzing openssl itself.
Using sha1sum via a pipe is too slow.

Test Plan: n/a

Reviewers: chandlerc

Reviewed By: chandlerc

Subscribers: majnemer, llvm-commits

Differential Revision: http://reviews.llvm.org/D9733

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237400 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Fuzzer/FuzzerInternal.h

@@ -44,6 +44,11 @@ std::string Hash(const Unit &U);
 void SetTimer(int Seconds);
 void PrintFileAsBase64(const std::string &Path);
 
+// Private copy of SHA1 implementation.
+static const int kSHA1NumBytes = 20;
+// Computes SHA1 hash of 'Len' bytes in 'Data', writes kSHA1NumBytes to 'Out'.
+void ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out);
+
 int NumberOfCpuCores();
 
 class Fuzzer {