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}"
@@ -471,13 +473,23 @@
 
 
 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
 }