libvpx: Pull from upstream

source/libvpx/build/make/configure.sh

 #!/bin/sh
 ##
 ##  configure.sh
 ##
 ##  This script is sourced by the main configure script and contains
 ##  utility functions and other common bits that aren't strictly libvpx
 ##  related.
 ##
 ##  This build system is based in part on the FFmpeg configure script.
 ##
@@ skipping 1305 matching lines @@
         fi
       fi
       ;;
   esac
 
   # glibc needs these
   if enabled linux; then
     add_cflags -D_LARGEFILE_SOURCE
     add_cflags -D_FILE_OFFSET_BITS=64
   fi
-
-  # append any user defined extra cflags
-  if [ -n "${extra_cflags}" ] ; then
-    check_add_cflags ${extra_cflags} || \
-    die "Requested extra CFLAGS '${extra_cflags}' not supported by compiler"
-  fi
 }
 
 process_toolchain() {
   process_common_toolchain
 }
 
 print_config_mk() {
   saved_prefix="${prefix}"
   prefix=$1
   makefile=$2
@@ skipping 81 matching lines @@
   # Prepare the PWD for building.
   for f in ${OOT_INSTALLS}; do
     install -D "${source_path}/$f" "$f"
   done
   fi
   cp "${source_path}/build/make/Makefile" .
 
   clean_temp_files
   true
 }