Upstream: not yet

Fix configure to accept "--prefix=" (a blank prefix).

--- libvpx-0.9.1/build/make/configure.sh.orig	2010-06-17 09:08:56.000000000 -0400
+++ libvpx-0.9.1/build/make/configure.sh	2010-09-23 14:27:48.000000000 -0400
@@ -444,6 +444,8 @@
         ;;
         --prefix=*)
         prefix="${optval}"
+        # Distinguish between "prefix not set" and "prefix set to ''"
+        prefixset=1
         ;;
         --libdir=*)
         libdir="${optval}"
@@ -587,13 +587,23 @@ process_cmdline() {
 }
 
 post_process_common_cmdline() {
-  prefix="${prefix:-/usr/local}"
+  if [ "$prefixset" != "1" ]
+  then
+      prefix=/usr/local
+  fi
+
+  # Strip trailing slash
   prefix="${prefix%/}"
+
   libdir="${libdir:-${prefix}/lib}"
   libdir="${libdir%/}"
-  if [ "${libdir#${prefix}}" = "${libdir}" ]; then
-    die "Libdir ${libdir} must be a subdirectory of ${prefix}"
-  fi
+
+  case "$libdir" in
+      "${prefix}/"*) ;;
+      *)
+          die "Libdir ${libdir} must be a subdirectory of ${prefix}"
+          ;;
+  esac
 }
 
 post_process_cmdline() {