Fix the git_master_bazel mixed build breakage.

There is no cflags defined for cortex-a9 CPU variant, set it to ArmGenericCflags to fix the mixed build breakage for now.

Bug: 258397103
Test: m com.android.build --bazel-mode-staging
Change-Id: I79a9877846ced6334c09a4f5caf115c436f600e6
diff --git a/cc/config/arm_device.go b/cc/config/arm_device.go
index b53a097..981d1ea 100644
--- a/cc/config/arm_device.go
+++ b/cc/config/arm_device.go
@@ -222,6 +222,7 @@
 		"":               "${config.ArmGenericCflags}",
 		"cortex-a7":      "${config.ArmCortexA7Cflags}",
 		"cortex-a8":      "${config.ArmCortexA8Cflags}",
+		"cortex-a9":      "${config.ArmGenericCflags}",
 		"cortex-a15":     "${config.ArmCortexA15Cflags}",
 		"cortex-a53":     "${config.ArmCortexA53Cflags}",
 		"cortex-a53.a57": "${config.ArmCortexA53Cflags}",