[ci] Enable -Werror=unused (#862)

.travis.yml

@@ -6,8 +6,8 @@ language: cpp
 env:
   global:
     - CPPFLAGS=""
-    - CFLAGS="-Werror -Werror=unused-function"
-    - CXXFLAGS="-Werror -Werror=unused-function -Wno-deprecated-register" # glib uses register and clang raises a warning
+    - CFLAGS="-Werror -Werror=unused -Werror=unused-function"
+    - CXXFLAGS="-Werror -Werror=unused -Werror=unused-function -Wno-deprecated-register" # glib uses register and clang raises a warning
     - CONFIGURE_OPTS="--with-freetype --with-glib --with-gobject --with-cairo --with-icu --with-graphite2"
     - NOCONFIGURE=1
     # COVERITY_SCAN_TOKEN

src/hb-ot-glyf-table.hh

@@ -299,7 +299,6 @@ struct glyf
         return true;
       else if (num_contours > 0)
       {
-        unsigned int glyph_len = *end_offset - start_offset;
         /* simple glyph w/contours, possibly trimmable */
         glyph += GlyphHeader::static_size + 2 * num_contours;