Use -Werror in external/libhevc

* Keep constant-conversion warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I4b956b73654029be940f911a4741be922fb3559b

Android.bp

@@ -8,6 +8,11 @@ cc_library_static {
 
         "-O3",
         "-DANDROID",
+        "-Wall",
+        "-Werror",
+        // common/x86/ihevc_sao_ssse3_intr.c: implicit conversion from
+        // 'int' to 'char' changes value from 128 to -128
+        "-Wno-error=constant-conversion",
     ],
 
     export_include_dirs: [

test/decoder.mk

@@ -5,7 +5,9 @@ include $(CLEAR_VARS)
 LOCAL_MODULE    := hevcdec
 LOCAL_MODULE_TAGS := optional
 
-LOCAL_CFLAGS := -DPROFILE_ENABLE -DARM  -fPIC -DMD5_DISABLE
+LOCAL_CFLAGS := \
+    -DPROFILE_ENABLE -DARM  -fPIC -DMD5_DISABLE \
+    -Wall -Werror
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/../decoder $(LOCAL_PATH)/../common $(LOCAL_PATH)/
 LOCAL_SRC_FILES := decoder/main.c
 LOCAL_STATIC_LIBRARIES := libhevcdec