Suppress warnings for Bazel third_party deps (#1054)

These warnings occur when building with gcc 7.3.0.

bazel/third_party/cairo/cairo.BUILD

@@ -273,6 +273,7 @@ cc_library(
         "-D_REENTRANT",
         "-Wno-attributes",
         "-Wno-cpp",
+        "-Wno-int-in-bool-context",
         "-Wno-maybe-uninitialized",
         "-Wno-misleading-indentation",
         "-Wno-strict-aliasing",

bazel/third_party/zlib.BUILD

@@ -46,5 +46,8 @@ cc_library(
         "zutil.h",
     ],
     hdrs = ["zlib.h"],
+    copts = [
+        "-Wno-implicit-function-declaration",
+    ],
     includes = ["."],
 )