Change comments to remark on script not being needed for clang >= 5.1

configure.ac

@@ -80,7 +80,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [[
 AC_MSG_RESULT([$CLANG])
 AS_IF([test "x$CLANG" == "xyes"], [CLANG_FLAGS=-Qunused-arguments])
 
-# We want to check for compiler flag support, but there is no way to make
+# We want to check for compiler flag support. Prior to clang v5.1, there was no way to make
 # clang's "argument unused" warning fatal.  So we invoke the compiler through a
 # wrapper script that greps for this message.
 saved_CC="$CC"

scripts/wrap-compiler-for-flag-check

@@ -3,12 +3,16 @@
 # From kmcallister: 
 # https://github.com/kmcallister/autoharden/blob/efaf5a16612589808c276a11536ea9a47071f74b/scripts/wrap-compiler-for-flag-check
 
-# There is no way to make clang's "argument unused" warning fatal.  So when
-# configure checks for supported flags, it runs $CC, $CXX, $LD via this
-# wrapper.
+# Prior to clang v5.1, there was no way to make
+# clang's "argument unused" warning fatal.  This
+# wrapper script that greps for this warning message. Newer clang's have no issues.
 #
 # Ideally the search string would also include 'clang: ' but this output might
 # depend on clang's argv[0].
+#
+# This file is in the public domain.
+set -o errexit
+set -o nounset
 
 if out=`"$@" 2>&1`; then
   echo "$out"