Enable -Werror by default

gprof/configure

@@ -859,6 +859,7 @@ Optional Features:
   --disable-nls           do not use Native Language Support
   --enable-maintainer-mode  enable make rules and dependencies not useful
 			  (and sometimes confusing) to the casual installer
+  --enable-error-on-warning    treat compile warnings as errors
   --enable-build-warnings Enable build-time compiler warnings if gcc is used
 
 Optional Packages:
@@ -3809,7 +3810,7 @@ test x"$pic_mode" = xno && libtool_flags="$libtool_flags --prefer-non-pic"
 case $host in
 *-*-irix6*)
   # Find out which ABI we are using.
-  echo '#line 3812 "configure"' > conftest.$ac_ext
+  echo '#line 3813 "configure"' > conftest.$ac_ext
   if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   (eval $ac_compile) 2>&5
   ac_status=$?
@@ -8287,6 +8288,26 @@ done
 
 
 build_warnings="-W -Wall -Wstrict-prototypes -Wmissing-prototypes"
+
+# Check whether --enable-error-on-warning or --disable-error-on-warning was given.
+if test "${enable_error_on_warning+set}" = set; then
+  enableval="$enable_error_on_warning"
+  case "${enableval}" in
+     yes | y) ERROR_ON_WARNING="yes" ;;
+     no | n)  ERROR_ON_WARNING="no" ;;
+     *) { { echo "$as_me:$LINENO: error: bad value ${enableval} for --enable-error-on-warning" >&5
+echo "$as_me: error: bad value ${enableval} for --enable-error-on-warning" >&2;}
+   { (exit 1); exit 1; }; } ;;
+   esac
+fi;
+
+# Enable -Werror by default, suppressing it only for --disable-error-on-warning
+# or --disable-build-warnings.
+if test "${ERROR_ON_WARNING}" != no
+then
+  build_warnings="$build_warnings -Werror"
+fi
+
 # Check whether --enable-build-warnings or --disable-build-warnings was given.
 if test "${enable_build_warnings+set}" = set; then
   enableval="$enable_build_warnings"