Don't #include <sys/syscall.h> under Fuchsia, which doesn't provide it.

Previous Fuchsia SDK versions provide an empty header file, for
convenience, but this is no longer the case.

Change-Id: Ica8d23cc38664b3ebe7093606da4c669d6043c73
Reviewed-on: https://chromium-review.googlesource.com/571763Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46688}

src/base/platform/platform-posix.cc

@@ -57,7 +57,7 @@
 #include <sys/prctl.h>  // NOLINT, for prctl
 #endif
 
-#ifndef _AIX
+#if !defined(_AIX) && !defined(V8_OS_FUCHSIA)
 #include <sys/syscall.h>
 #endif
 

src/libsampler/sampler.cc

@@ -13,7 +13,7 @@
 #include <signal.h>
 #include <sys/time.h>
 
-#if !V8_OS_QNX && !V8_OS_AIX
+#if !V8_OS_QNX && !V8_OS_FUCHSIA && !V8_OS_AIX
 #include <sys/syscall.h>  // NOLINT
 #endif