Remove clang 3.7 and fuchsia specific flags

since clang 3.7 dates to 2015 and is obsolete.
Fuchsia has been fixed: https://issues.fuchsia.dev/issues/42051468

BUG=None

Change-Id: Id0966c3f4acfb1756eab4e2e6f0dbe52d70ecd76
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/362571
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@meta.com>
Cr-Commit-Position: refs/heads/main@{#43044}

BUILD.gn

@@ -419,19 +419,11 @@ config("common_config") {
     }
 
     if (is_clang) {
-      cflags += [ "-Wc++11-narrowing" ]
-
-      if (!is_fuchsia) {
-        # Compiling with the Fuchsia SDK results in Wundef errors
-        # TODO(bugs.fuchsia.dev/100722): Remove from (!is_fuchsia) branch when
-        # Fuchsia build errors are fixed.
-        cflags += [ "-Wundef" ]
-      }
-
-      if (!is_nacl) {
-        # Flags NaCl (Clang 3.7) do not recognize.
-        cflags += [ "-Wunused-lambda-capture" ]
-      }
+      cflags += [
+        "-Wc++11-narrowing",
+        "-Wundef",
+        "-Wunused-lambda-capture",
+      ]
     }
 
     if (is_win && !is_clang) {