Use libc++ for all XSAN builds

Docs-Preview: https://skia.org/?cl=107306
Bug: oss-fuzz:6347
Change-Id: I59c3b1b2e693fd97be0091ba2df406f51461fd10
Reviewed-on: https://skia-review.googlesource.com/107306
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index b255eba..7c35f71 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -249,12 +249,12 @@
     ]
     if (!is_win) {
       cflags += [ "-fno-omit-frame-pointer" ]
+      cflags_cc += [ "-stdlib=libc++" ]
+      ldflags += [ "-stdlib=libc++" ]
     }
     ldflags += [ "-fsanitize=$sanitizers" ]
     if (sanitizers == "memory") {
       cflags += [ "-fsanitize-memory-track-origins" ]
-      cflags_cc += [ "-stdlib=libc++" ]
-      ldflags += [ "-stdlib=libc++" ]
     }
   }
 }