Prepare for |is_posix| switch in the Fuchsia build

|is_posix| will be switched to false for Fuchsia, this is a preliminary change.

Bug: chromium:812974
Change-Id: I3bfda3e056ad1e5229834286ce5d095d9204a428
Reviewed-on: https://webrtc-review.googlesource.com/65782
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#22753}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 92088b0..80e4455 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -452,7 +452,7 @@
     libs += [ "log" ]
   }
 
-  if (is_posix) {
+  if (is_posix || is_fuchsia) {
     sources += [ "file_posix.cc" ]
   }
 
@@ -1019,7 +1019,7 @@
     defines += [ "_CRT_NONSTDC_NO_DEPRECATE" ]
   }
 
-  if (is_posix) {
+  if (is_posix || is_fuchsia) {
     sources += [
       "ifaddrs_converter.cc",
       "ifaddrs_converter.h",
@@ -1353,7 +1353,7 @@
         "win32window_unittest.cc",
       ]
     }
-    if (is_posix) {
+    if (is_posix || is_fuchsia) {
       sources += [
         "openssladapter_unittest.cc",
         "ssladapter_unittest.cc",