generate-emscripten-symbols.sh: allows the lib path to be overridden

dist-build/generate-emscripten-symbols.sh

@@ -2,6 +2,8 @@
 
 set -e
 
+LIBSODIUM=${LIBSODIUM:-/tmp/sodium/lib/libsodium.27.dylib}
+
 symbols() {
   {
     SUMO="$1"
@@ -17,8 +19,8 @@ symbols() {
       fi
     done < emscripten-symbols.def
 
-    /usr/bin/nm /usr/local/lib/libsodium.23.dylib | \
-    fgrep ' T _' | \
+    /usr/bin/nm "$LIBSODIUM" |
+      fgrep ' T _' |
       cut -d' ' -f3 | {
       while read symbol; do
         eval "found=\$defined_${symbol}"