Fix CLANG_EXTERNAL_CFLAGS logic

Should be neq instead of eq.

Test: build-full.ninja is now correct
Change-Id: I26c0aa84d9b54a8b19f19124978ac1d49bae7448
diff --git a/core/binary.mk b/core/binary.mk
index 6067615..2899d4d 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -407,7 +407,7 @@
 
 # Extra cflags for projects under external/ directory
 ifeq ($(my_clang),true)
-ifeq ($(filter external/%,$(LOCAL_PATH)),)
+ifneq ($(filter external/%,$(LOCAL_PATH)),)
     my_cflags += $(CLANG_EXTERNAL_CFLAGS)
 endif
 endif