getdeps: silence inherits via dominance warnings

Summary:
Previously, the Windows build was litered with warnings of the form (typo included):

  warning C4250: 'C1': inherits 'C2::C2::method' via dominance
  note: see declaration of 'C2::method'

Microsoft doesn't offer any recommendation, and the internet suggest that the
right `using` should silence it. That's unfortunately not the case, adding:
  using C2::method
In `C1` doesn't do anything, and the compiler still complains :(.

Since the warning appears to be non-actionable, and looks more like a
"notice" than a warning, let's just silence it.

Reviewed By: wez

Differential Revision: D21395095

fbshipit-source-id: ae661b3ed61303e6361b8a15d9e7c6b9627ea8c1

build/fbcode_builder/CMake/FBCompilerSettings.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
+
+# This file applies common compiler settings that are shared across
+# a number of Facebook opensource projects.
+# Please use caution and your best judgement before making changes
+# to these shared compiler settings in order to avoid accidentally
+# breaking a build in another project!
+
+if (WIN32)
+  include(FBCompilerSettingsMSVC)
+else()
+  include(FBCompilerSettingsUnix)
+endif()

build/fbcode_builder/CMake/FBCompilerSettingsMSVC.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
+
+# This file applies common compiler settings that are shared across
+# a number of Facebook opensource projects.
+# Please use caution and your best judgement before making changes
+# to these shared compiler settings in order to avoid accidentally
+# breaking a build in another project!
+
+add_compile_options(
+  /wd4250 # 'class1' : inherits 'class2::member' via dominance
+)

build/fbcode_builder/CMake/FBCompilerSettingsUnix.cmake

+# Copyright (c) Facebook, Inc. and its affiliates.
+
+# This file applies common compiler settings that are shared across
+# a number of Facebook opensource projects.
+# Please use caution and your best judgement before making changes
+# to these shared compiler settings in order to avoid accidentally
+# breaking a build in another project!
+
+set(CMAKE_CXX_FLAGS_COMMON "-g -Wall -Wextra -Wno-deprecated -Wno-deprecated-declarations")
+set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${CMAKE_CXX_FLAGS_COMMON}")
+set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${CMAKE_CXX_FLAGS_COMMON} -O3")