[libcxx] Support threads on Fuchsia

Differential Revision: https://reviews.llvm.org/D30278

llvm-svn: 296573
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 11d1770e14a73ffdaece5f3935db383b64df2c03
diff --git a/src/thread.cpp b/src/thread.cpp
index 74194ac..3f283c3 100644
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -24,9 +24,9 @@
 # endif // defined(BSD)
 #endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 
-#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__)
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__)
 # include <unistd.h>
-#endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__)
+#endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__)
 
 #if defined(__NetBSD__)
 #pragma weak pthread_create // Do not create libpthread dependency