Makefile/configure: add -Wunused-result check

Makefile

@@ -28,7 +28,10 @@ LANGUAGES ?= bg cs de en en_GB fr he hr it pl pt sv
 # Common compiler flags
 #
 
-CFLAGS  += -g -O2 -Wunused-result
+CFLAGS  += -g -O2
+ifeq ($(CONFIG_W_UNUSED_RESULT),yes)
+CFLAGS  += -Wunused-result
+endif
 CFLAGS  += -Wall -Werror -Wwrite-strings -Wno-deprecated-declarations
 CFLAGS  += -Wmissing-prototypes
 CFLAGS  += -fms-extensions -funsigned-char -fno-strict-aliasing

configure

@@ -116,6 +116,7 @@ check_cc || die 'No C compiler found'
 check_cc_header execinfo
 check_cc_option mmx
 check_cc_option sse2
+check_cc_optionW unused-result
 
 if check_cc '
 #if !defined(__clang__)

support/configure.inc

@@ -303,6 +303,26 @@ check_cc_option ()
   fi
 }
 
+# Check compiler option
+check_cc_optionW ()
+{
+  local opt=$1
+  local nam=$2
+  [ -z "$nam" ] && nam=$opt
+  nam=$(echo "W_$nam" | sed -e 's/-/_/')
+
+  printf "$TAB" "checking for cc -W$opt ..."
+
+  # Enable if supported
+  if check_cc "" -W${opt}; then
+    echo "ok"
+    enable $nam
+  else
+    echo "fail"
+    return 1
+  fi
+}
+
 # Check compiler library
 check_cc_lib ()
 {