Bug 1257870 - Require 1.5.0 --with-system-libvpx. r=glandium

WebRTC code requires VP9E_SET_NOISE_SENSITIVITY from vpx/vp8cx.h
which was added in 1.4. We could feature test, but gating on
the minimum version seems better given the m4 code is to be
replaced by python.

We also depend on VPX_MAX_LAYERS wich is part of the 1.5.0 release.
This dependency was added with an SVC support patch in May 2015,
bug 1237023.

Optional --enable-spatial-svc is handled by the work-around
in bug 1248335.

MozReview-Commit-ID: 79kg9JSFtJM

old-configure.in

@@ -4160,7 +4160,7 @@ if test -n "$MOZ_SYSTEM_LIBVPX"; then
     dnl === libvpx Version check ===
     dnl ============================
     dnl Check to see if we have a system libvpx package.
-    PKG_CHECK_MODULES(MOZ_LIBVPX, vpx >= 1.3.0)
+    PKG_CHECK_MODULES(MOZ_LIBVPX, vpx >= 1.5.0)
 
     CFLAGS="$CFLAGS $MOZ_LIBVPX_CFLAGS"
     LIBS="$LIBS $MOZ_LIBVPX_LIBS"