GN: detect is_clang, use it to switch Clang to warning blacklist.

gn/BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
   ar = "ar"
   cc = "cc"
   cxx = "c++"
 
   if (is_android) {
     ar = "$ndk/toolchains/$ndk_gccdir-4.9/prebuilt/$ndk_host/$ndk_target/bin/ar"
     cc = "$ndk/toolchains/llvm/prebuilt/$ndk_host/bin/clang"
     cxx = "$ndk/toolchains/llvm/prebuilt/$ndk_host/bin/clang++"
   }
 
   windk = ""
 
   extra_cflags = ""
   extra_cflags_c = ""
   extra_cflags_cc = ""
   extra_ldflags = ""
 
   cc_wrapper = ""
 }
 
+is_clang = exec_script("is_clang.py",
+                       [
+                         cc,
+                         cxx,
+                       ],
+                       "value")
+
 config("default") {
   asmflags = []
   cflags = []
   cflags_c = []
   cflags_cc = []
   defines = []
   ldflags = []
 
   if (is_win) {
     cflags += [
@@ skipping 26 matching lines @@
       "-Wno-unused-parameter",
     ]
     cflags_cc += [
       "-std=c++11",
       "-fno-exceptions",
       "-fno-threadsafe-statics",
       "-fvisibility-inlines-hidden",
 
       "-Wnon-virtual-dtor",
     ]
+    if (is_clang) {
+      cflags += [
+        "-Weverything",
+        "-Wno-unknown-warning-option",  # Let older Clangs ignore newer Clangs' warnings.
+      ]
+
+      # High priority to fix!
+      cflags += [
+        "-Wno-comma",
+        "-Wno-conditional-uninitialized",
+        "-Wno-covered-switch-default",
+        "-Wno-deprecated",
+        "-Wno-format-nonliteral",
+        "-Wno-over-aligned",
+        "-Wno-shadow",
+        "-Wno-shift-sign-overflow",
+        "-Wno-undefined-func-template",
+        "-Wno-undefined-reinterpret-cast",
+      ]
+
+      cflags += [
+        "-Wno-cast-align",
+        "-Wno-class-varargs",
+        "-Wno-conversion",
+        "-Wno-disabled-macro-expansion",
+        "-Wno-documentation",
+        "-Wno-documentation-unknown-command",
+        "-Wno-double-promotion",
+        "-Wno-exit-time-destructors",  # TODO: OK outside libskia
+        "-Wno-extra-semi",
+        "-Wno-float-conversion",
+        "-Wno-float-equal",
+        "-Wno-global-constructors",  # TODO: OK outside libskia
+        "-Wno-gnu-anonymous-struct",
+        "-Wno-gnu-zero-variadic-macro-arguments",
+        "-Wno-missing-prototypes",
+        "-Wno-missing-variable-declarations",
+        "-Wno-nested-anon-types",
+        "-Wno-newline-eof",
+        "-Wno-pedantic",
+        "-Wno-reserved-id-macro",
+        "-Wno-sign-conversion",
+        "-Wno-switch-enum",
+        "-Wno-undef",
+        "-Wno-unreachable-code",
+        "-Wno-unreachable-code-break",
+        "-Wno-unreachable-code-return",
+        "-Wno-unused-macros",
+        "-Wno-unused-member-function",
+      ]
+      cflags_cc += [
+        "-Wno-abstract-vbase-init",
+        "-Wno-range-loop-analysis",
+        "-Wno-weak-vtables",
+      ]
+
+      # We are unlikely to want to fix these.
+      cflags += [
+        "-Wno-implicit-fallthrough",
+        "-Wno-missing-noreturn",
+        "-Wno-old-style-cast",
+        "-Wno-padded",
+      ]
+      cflags_cc += [
+        "-Wno-c++98-compat",
+        "-Wno-c++98-compat-pedantic",
+      ]
+    }
   }
 
   if (current_cpu == "arm") {
     cflags += [
       "-march=armv7-a",
       "-mfpu=neon",
       "-mthumb",
     ]
   } else if (current_cpu == "mipsel") {
     cflags += [
@@ skipping 279 matching lines @@
   }
 
   tool("stamp") {
     command = "touch {{output}}"
   }
 
   tool("copy") {
     command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
   }
 }