libvpx: Pull from upstream

source/libvpx/build/make/rtcd.sh

 #!/bin/sh
 self=$0
 
 usage() {
   cat <<EOF >&2
 Usage: $self [options] FILE
 
 Reads the Run Time CPU Detections definitions from FILE and generates a
 C header file on stdout.
 
@@ skipping 191 matching lines @@
   cat <<EOF
 #ifndef ${include_guard}
 #define ${include_guard}
 
 #ifdef RTCD_C
 #define RTCD_EXTERN
 #else
 #define RTCD_EXTERN extern
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 $(process_forward_decls)
 
 $(declare_function_pointers c $ALL_ARCHS)
 
 void ${symbol:-rtcd}(void);
 EOF
 }
 
 common_bottom() {
   cat <<EOF
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
 #endif
 EOF
 }
 
 x86() {
   determine_indirection c $ALL_ARCHS
 
   # Assign the helper variable for each enabled extension
   for opt in $ALL_ARCHS; do
     uc=$(echo $opt | tr '[a-z]' '[A-Z]')
@@ skipping 122 matching lines @@
     arm
     ;;
   armv7)
     ALL_ARCHS=$(filter edsp media neon)
     arm
     ;;
   *)
     unoptimized
     ;;
 esac