Fix unused-command-line-argument warning

Limit -msse2 and -mpopcnt flags to x86/x86_64 linux targets only.

Test: build
Bug: 197177755
Change-Id: Ia213f0a8bb836e765822a68770e2fee6407c1bcd
diff --git a/build/Android.bp b/build/Android.bp
index 21858db..34f11fe 100644
--- a/build/Android.bp
+++ b/build/Android.bp
@@ -211,13 +211,23 @@
                 // Bug: 15446488. We don't omit the frame pointer to work around
                 // clang/libunwind bugs that cause SEGVs in run-test-004-ThreadStress.
                 "-fno-omit-frame-pointer",
-                // The build assumes that all our x86/x86_64 hosts (such as buildbots and developer
-                // desktops) support at least sse4.2/popcount. This firstly implies that the ART
-                // runtime binary itself may exploit these features. Secondly, this implies that
-                // the ART runtime passes these feature flags to dex2oat and JIT by calling the
-                // method InstructionSetFeatures::FromCppDefines(). Since invoking dex2oat directly
-                // does not pick up these flags, cross-compiling from a x86/x86_64 host to a
-                // x86/x86_64 target should not be affected.
+            ],
+        },
+        // The build assumes that all our x86/x86_64 hosts (such as buildbots and developer
+        // desktops) support at least sse4.2/popcount. This firstly implies that the ART
+        // runtime binary itself may exploit these features. Secondly, this implies that
+        // the ART runtime passes these feature flags to dex2oat and JIT by calling the
+        // method InstructionSetFeatures::FromCppDefines(). Since invoking dex2oat directly
+        // does not pick up these flags, cross-compiling from a x86/x86_64 host to a
+        // x86/x86_64 target should not be affected.
+        linux_x86: {
+            cflags: [
+                "-msse4.2",
+                "-mpopcnt",
+            ],
+        },
+        linux_x86_64: {
+            cflags: [
                 "-msse4.2",
                 "-mpopcnt",
             ],