Disable strict-aliasing for gyp

In gn, strict aliasing is disabled anyway. Enabling it for gyp can cause
the compilation to fail on bots that still use gyp, or (even worse) can
lead to miscompilation because the compiler exploits strict aliasing
assumptions.

R=machenbach@chromium.org

Bug: chromium:628560
Change-Id: Ib756b8126a10d52f8c807ceda42dfc6dbda80ea6
Reviewed-on: https://chromium-review.googlesource.com/571806Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46678}

gypfiles/standalone.gypi

@@ -779,6 +779,9 @@
               # that signed overflow does not occur. Generates false positives
               # (see http://crbug.com/v8/6341).
               "-Wno-strict-overflow",
+              # Don't rely on strict aliasing; v8 does weird pointer casts all
+              # over the place.
+              '-fno-strict-aliasing',
             ],
           }],
           [ 'clang==1 and (v8_target_arch=="x64" or v8_target_arch=="arm64" \