[fuchsia] Stop overriding safestack & shadow-call-stack settings.

Fuchsia builds have been forcibly disabling safestack because it broke
V8 tests under Fuchsia, and forcibly enabling shadow-call-stack in
advance of it becoming the toolchain default, to gauge size impact.

Enabling shadow-call-stack under x64 is not recommended and breaks code
which uses C++ exceptions, which is true of some V8 code & tests.

Since the toolchain default should now be correct, remove the overrides
entirely.

Bug: 1028617, 821951
Change-Id: I36333f8cff5ea62584032a802337cdeb95f33466
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014407
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734110}

build/config/fuchsia/BUILD.gn

@@ -49,14 +49,6 @@ 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" ]
 }