libvpx: Add VP9 decoder.

source/libvpx/build/make/configure.sh

Index: source/libvpx/build/make/configure.sh
===================================================================
--- source/libvpx/build/make/configure.sh	(revision 172621)
+++ source/libvpx/build/make/configure.sh	(working copy)
@@ -277,6 +277,7 @@
 # Toolchain Check Functions
 #
 check_cmd() {
+    enabled external_build && return
     log "$@"
     "$@" >>${logfile} 2>&1
 }
@@ -435,10 +436,10 @@
 EOF
 
     if enabled rvct; then cat >> $1 << EOF
-fmt_deps = sed -e 's;^__image.axf;\$(dir \$@)\$(notdir \$<).o \$@;' #hide
+fmt_deps = sed -e 's;^__image.axf;\$\${@:.d=.o} \$\$@;' #hide
 EOF
     else cat >> $1 << EOF
-fmt_deps = sed -e 's;^\([a-zA-Z0-9_]*\)\.o;\$(dir \$@)\1\$(suffix \$<).o \$@;'
+fmt_deps = sed -e 's;^\([a-zA-Z0-9_]*\)\.o;\$\${@:.d=.o} \$\$@;'
 EOF
     fi
 
@@ -1175,9 +1176,6 @@
         ;;
     esac
 
-    # for sysconf(3) and friends.
-    check_header unistd.h
-
     # glibc needs these
     if enabled linux; then
         add_cflags -D_LARGEFILE_SOURCE