Revert "[Fuchsia] Stop enabling shadow-call-stack explicitly"

This reverts commit 3ee16746.

Reason for revert: HeapTests are failing crbug.com/1023716

Original change's description:
> [Fuchsia] Stop enabling shadow-call-stack explicitly
> 
> shadow-call-stack is enabled by default on Fuchsia now, so we no longer
> need to enable it explicitly.
> 
> Bug: 821951
> Change-Id: I221bc557bf93dfd5bf7c1659f7f8dfc32129c6b1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898631
> Commit-Queue: Wez <wez@chromium.org>
> Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
> Reviewed-by: Wez <wez@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#714312}

TBR=wez@chromium.org,sergeyu@chromium.org

Change-Id: I7e8467363407c8ce1738ae83f31e7c543d3e9144
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 821951
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911066Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714393}

build/config/fuchsia/BUILD.gn

@@ -49,6 +49,14 @@ config("compiler") {
   # Add SDK lib dir for -lfdio above.
   lib_dirs = [ "${fuchsia_sdk}/arch/${current_cpu}/lib" ]
 
+  # TODO(crbug.com/821951): Clang enables SafeStack by default when targeting
+  # Fuchsia, but it breaks some tests, notably in V8.
+  # Force the toolchain to use shadow-call-stack instead, until that is default.
+  cflags += [
+    "-fno-sanitize=safe-stack",
+    "-fsanitize=shadow-call-stack",
+  ]
+
   libs = [ "zircon" ]
 }