autoconf: Tolerate missing file when grepping.

Currently we die when grepping for compatibility strings if the
file does not exist.  Since this can be a valid situation when
files are added in later versions, we shouldn't kill the build.
Instead, note that the file doesn't exist but otherwise treat it
as if the string was not found.

diff --git a/acinclude.m4 b/acinclude.m4
index f1322fa..0af7fd0 100644 (file)
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -108,21 +108,26 @@ dnl
 dnl Greps FILE for REGEX.  If it matches, runs IF-MATCH, otherwise IF-NO-MATCH.
 AC_DEFUN([OVS_GREP_IFELSE], [
   AC_MSG_CHECKING([whether $2 matches in $1])
-  grep '$2' $1 >/dev/null 2>&1
-  status=$?
-  case $status in
-    0) 
-      AC_MSG_RESULT([yes])
-      $3
-      ;;
-    1) 
-      AC_MSG_RESULT([no])
-      $4
-      ;;
-    *) 
-      AC_MSG_ERROR([grep exited with status $status]) 
-      ;;
-  esac
+  if test -f $1; then
+    grep '$2' $1 >/dev/null 2>&1
+    status=$?
+    case $status in
+      0) 
+        AC_MSG_RESULT([yes])
+        $3
+        ;;
+      1) 
+        AC_MSG_RESULT([no])
+        $4
+        ;;
+      *) 
+        AC_MSG_ERROR([grep exited with status $status])
+        ;;
+    esac
+  else
+    AC_MSG_RESULT([file not found])
+    $4
+  fi
 ])
 
 dnl OVS_DEFINE(NAME)