In assembler check, try to use gas first (based on a patch by Robert
Lunnon).

diff --git a/configure b/configure
index 0b988e3..7ae64e4 100755
--- a/configure
+++ b/configure
@@ -4189,8 +4189,10 @@
 fi
 
 if test -n "$ac_tool_prefix"; then
-  # Extract the first word of "${ac_tool_prefix}as", so it can be a program name with args.
-set dummy ${ac_tool_prefix}as; ac_word=$2
+  for ac_prog in gas as
+  do
+    # Extract the first word of "$ac_tool_prefix$ac_prog", so it can be a program name with args.
+set dummy $ac_tool_prefix$ac_prog; ac_word=$2
 echo "$as_me:$LINENO: checking for $ac_word" >&5
 echo $ECHO_N "checking for $ac_word... $ECHO_C" >&6
 if test "${ac_cv_prog_AS+set}" = set; then
@@ -4206,7 +4208,7 @@
   test -z "$as_dir" && as_dir=.
   for ac_exec_ext in '' $ac_executable_extensions; do
   if $as_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
-    ac_cv_prog_AS="${ac_tool_prefix}as"
+    ac_cv_prog_AS="$ac_tool_prefix$ac_prog"
     echo "$as_me:$LINENO: found $as_dir/$ac_word$ac_exec_ext" >&5
     break 2
   fi
@@ -4224,11 +4226,15 @@
 echo "${ECHO_T}no" >&6
 fi
 
+    test -n "$AS" && break
+  done
 fi
-if test -z "$ac_cv_prog_AS"; then
+if test -z "$AS"; then
   ac_ct_AS=$AS
-  # Extract the first word of "as", so it can be a program name with args.
-set dummy as; ac_word=$2
+  for ac_prog in gas as
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
 echo "$as_me:$LINENO: checking for $ac_word" >&5
 echo $ECHO_N "checking for $ac_word... $ECHO_C" >&6
 if test "${ac_cv_prog_ac_ct_AS+set}" = set; then
@@ -4244,14 +4250,13 @@
   test -z "$as_dir" && as_dir=.
   for ac_exec_ext in '' $ac_executable_extensions; do
   if $as_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
-    ac_cv_prog_ac_ct_AS="as"
+    ac_cv_prog_ac_ct_AS="$ac_prog"
     echo "$as_me:$LINENO: found $as_dir/$ac_word$ac_exec_ext" >&5
     break 2
   fi
 done
 done
 
-  test -z "$ac_cv_prog_ac_ct_AS" && ac_cv_prog_ac_ct_AS="as"
 fi
 fi
 ac_ct_AS=$ac_cv_prog_ac_ct_AS
@@ -4263,9 +4268,11 @@
 echo "${ECHO_T}no" >&6
 fi
 
+  test -n "$ac_ct_AS" && break
+done
+test -n "$ac_ct_AS" || ac_ct_AS="as"
+
   AS=$ac_ct_AS
-else
-  AS="$ac_cv_prog_AS"
 fi
 
 if test -n "$ac_tool_prefix"; then