Don't include <sys/sysctl.h> on CloudABI.

As CloudABI does not provide sysctl(), this header is not present. Make
thread.cpp build correctly (and pass all tests) by not including the header.

llvm-svn: 231768
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: cda27e8197fc15da162a445b3aaedff5a006a462
diff --git a/src/thread.cpp b/src/thread.cpp
index 6aad558..bd27f28 100644
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -17,9 +17,9 @@
 #include "limits"
 #include <sys/types.h>
 #if !defined(_WIN32)
-# if !defined(__sun__) && !defined(__linux__) && !defined(_AIX) && !defined(__native_client__)
+# if !defined(__sun__) && !defined(__linux__) && !defined(_AIX) && !defined(__native_client__) && !defined(__CloudABI__)
 #   include <sys/sysctl.h>
-# endif // !defined(__sun__) && !defined(__linux__) && !defined(_AIX) && !defined(__native_client__)
+# endif // !defined(__sun__) && !defined(__linux__) && !defined(_AIX) && !defined(__native_client__) && !defined(__CloudABI__)
 # include <unistd.h>
 #endif // !_WIN32