os2-buildbot.sh: Use the 64-bit Watcom binaries.

GitHub Actions is a 64-bit Ubuntu instance. It was only using the 32-bit
binaries because our buildbot put this on the 32-bit Linux host to spread
the CPU load around more evenly.

build-scripts/os2-buildbot.sh

@@ -12,7 +12,7 @@ if [ -z "$WATCOM" ]; then
     echo "This is often something like '/usr/local/share/watcom'" 1>&2
     exit 1
 fi
-export PATH="$WATCOM/binl:$PATH"
+export PATH="$WATCOM/binl64:$PATH"
 
 ZIPFILE="$1"
 if [ -z $1 ]; then