Define PRIVATE and add it to all global symbols so we don't export assembly functions.

libvpx/source/libvpx/vpx_ports/x86_abi_support.asm

Index: libvpx/source/libvpx/vpx_ports/x86_abi_support.asm
diff --git a/libvpx/source/libvpx/vpx_ports/x86_abi_support.asm b/libvpx/source/libvpx/vpx_ports/x86_abi_support.asm
index be64cd7c708020a09a726a655c4b8e86e77efb75..49ff0091e72272af9d3c07a05a78cce643e22697 100644
--- a/libvpx/source/libvpx/vpx_ports/x86_abi_support.asm
+++ b/libvpx/source/libvpx/vpx_ports/x86_abi_support.asm
@@ -92,6 +92,28 @@
 %define sym(x) _ %+ x
 %endif
 
+
+; PRIVATE
+; Macro for the attribute to hide a global symbol for the target ABI.
+;
+; Chromium doesn't like exported global symbols due to symbol clashing with
+; plugins among other things.
+;
+; Requires Chromium's patched copy of yasm:
+;   http://src.chromium.org/viewvc/chrome?view=rev&revision=73761
+;   http://www.tortall.net/projects/yasm/ticket/236
+;
+%ifidn   __OUTPUT_FORMAT__,elf32
+%define PRIVATE :hidden
+%elifidn __OUTPUT_FORMAT__,elf64
+%define PRIVATE :hidden
+%elifidn __OUTPUT_FORMAT__,x64
+%define PRIVATE
+%else
+%define PRIVATE :private_extern
+%endif
+
+
 ; arg()
 ; Return the address specification of the given argument
 ;