Windows: Build the double_conversion target as C++17 (fixes issue #2819)

This works around a bug in the Visual C++ standard library where the
std::is_integral templates are exported instead of inlined when building
with C++14. See also https://bugs.llvm.org/show_bug.cgi?id=42027.

patch/patch.cfg

@@ -477,5 +477,11 @@ patches = [
     # Windows: Fix ImportError: No module named win32file
     # https://bugs.chromium.org/p/chromium/issues/detail?id=1033106#c7
     'name': 'win_tool_wrapper_1033106',
+  },
+  {
+    # Windows: Build the double_conversion target as C++17 to avoid export of
+    # std::is_integral templates that should be inlined.
+    # https://bitbucket.org/chromiumembedded/cef/issues/2819
+    'name': 'win_double_conversion_2819',
   }
 ]

patch/patches/win_double_conversion_2819.patch

@@ -0,0 +1,16 @@
+diff --git base/third_party/double_conversion/BUILD.gn base/third_party/double_conversion/BUILD.gn
+index 0083efdcd9c8..6f647c31e28a 100644
+--- base/third_party/double_conversion/BUILD.gn
++++ base/third_party/double_conversion/BUILD.gn
+@@ -9,6 +9,11 @@ config("config") {
+     "-Wno-unused-const-variable",
+     "-Wno-unused-function",
+   ]
++
++  # Build as C++17 to avoid export of templates that should be inlined.
++  if (is_win) {
++    cflags_cc = [ "/std:c++17" ]
++  }
+ }
+ 
+ static_library("double_conversion") {