gen_msvs_proj.sh: avoid asm object name collisions

fixes link under vs9; this is the same change as:
dbf6e3f gen_msvs_vcxproj.sh: Avoid object name collisions.

Change-Id: I2a188c9024d0605e60e5e03ddcef1a25e7e53585

build/make/gen_msvs_proj.sh

@@ -73,6 +73,10 @@ generate_filter() {
                 open_tag File RelativePath="$f"
 
                 if [ "$pat" == "asm" ] && $asm_use_custom_step; then
+                    # Avoid object file name collisions, i.e. vpx_config.c and
+                    # vpx_config.asm produce the same object file without
+                    # this additional suffix.
+                    objf=${objf%.obj}_asm.obj
                     for plat in "${platforms[@]}"; do
                         for cfg in Debug Release; do
                             open_tag FileConfiguration \