FS-8867: do hidden visibility on vpx as we don't want symbols leaking out of…

FS-8867: do hidden visibility on vpx as we don't want symbols leaking out of libfreeswitch, and we get relocation error on a vpx symbol anyways

Makefile.am

@@ -516,7 +516,7 @@ libs/libzrtp/libzrtp.a:
 	cd libs/libzrtp && $(MAKE)
 
 libs/libvpx/Makefile:
-	cd libs/libvpx && sh ./configure --enable-pic --disable-docs --disable-examples --disable-install-bins --disable-install-srcs --disable-unit-tests
+	cd libs/libvpx && sh ./configure --enable-pic --disable-docs --disable-examples --disable-install-bins --disable-install-srcs --disable-unit-tests --extra-cflags="-fvisibility=hidden"
 
 libs/libvpx/libvpx.a: libs/libvpx/Makefile
 	@cd libs/libvpx && $(MAKE)