Use -Werror in external/libmicrohttpd

* Suppressed warnings: sign-compare, tautological-constant-out-of-range-compare,
     unused-parameter, unused-variable.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I59aec03654591e2fa6fd9eaed4fd855e440e23b2
diff --git a/Android.mk b/Android.mk
index 10e7f6f..84ebd2d 100644
--- a/Android.mk
+++ b/Android.mk
@@ -18,7 +18,13 @@
 include $(CLEAR_VARS)
 
 LOCAL_MODULE := libmicrohttpd
-LOCAL_CFLAGS := -Wno-sign-compare -Wno-unused-parameter
+LOCAL_CFLAGS := \
+    -Wall -Werror \
+    -Wno-sign-compare \
+    -Wno-tautological-constant-out-of-range-compare \
+    -Wno-unused-parameter \
+    -Wno-unused-variable \
+
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/src/include
 
 LOCAL_C_INCLUDES := \