Compile with GCC 7.2.0.

This suppresses the noexcept-type warning, since Skia doesn't have a
stable ABI in any event. GCC now warns on more printf style formats,
so we have to hide our bad test formats a little better. GCC now
also warns on implicit enum to bool conversions, which did catch two
issues.

Change-Id: Ib81769c421757186506873f0fe298ecd0106ae87
Reviewed-on: https://skia-review.googlesource.com/114263
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index 97bb030..f75637a 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -299,7 +299,10 @@
       "-Wno-deprecated-declarations",
       "-Wno-maybe-uninitialized",
     ]
-    cflags_cc += [ "-Wnon-virtual-dtor" ]
+    cflags_cc += [
+      "-Wnon-virtual-dtor",
+      "-Wno-noexcept-type",
+    ]
   }
 
   if (is_clang) {