Escaping compiler and linker options causes wrong behaviour

Created by: shybovycha

On OSX the -framework is a valid linker CLI flag, which could be set in Buck with usual cxx_binary / cxx_library rules which, in combination with platform_linker_flags allows to go away from platform-dependent targets.

But due to argument escaping turned on by default, clang complains about unknown arguments:

cxx_binary(
  name = 'main',
  srcs = [ 'main.cpp' ],
  platform_linker_flags = [
    ('macos', [
      '-framework $SDKROOT/System/Library/Frameworks/Cocoa.framework',
    ])
  ],
)

gives

unknown argument: '-framework $SDKROOT/System/Library/Frameworks/Cocoa.framework'

The behaviors defined in buck sources do not consider any way to disable this escaping. I tried getting around this by defining a new option for [cxx] section in .buckconfig, but I could not get my head around com.facebook.buck.cxx.CxxPrepareForLinkStep - simply can't see a good way to pass the option there.