gen_msvs_vcxproj.sh: Avoid object name collisions.

Fixes the following warning:
warning LNK4042: object specified more than once; extras ignored

Change-Id: Icee24073be774e7f7902587449fb90a42ab16b6f

build/make/gen_msvs_vcxproj.sh

@@ -156,6 +156,10 @@ generate_filter() {
                 objf=$(echo ${f%.*}.obj | sed -e 's/^[\./]\+//g' -e 's,/,_,g')
 
                 if ([ "$pat" == "asm" ] || [ "$pat" == "s" ]) && $asm_use_custom_step; then
+                    # Avoid object file name collisions, i.e. vpx_config.c and
+                    # vpx_config.asm produce the same object file without
+                    # this additional suffix.
+                    objf=${objf%.obj}_asm.obj
                     open_tag CustomBuild \
                         Include=".\\$f"
                     for plat in "${platforms[@]}"; do