[Linux] Fix pkg-config trailing space causing premake to output an extra empty library -l

Fixes #1868

tools/build/scripts/pkg_config.lua

@@ -24,8 +24,10 @@ function pkg_config.lflags(lib)
   local output = ({os.outputof("pkg-config --libs-only-l "..lib)})[1]
   for k, flag in next, string.explode(output, " ") do
     -- remove "-l"
+    if flag ~= "" then
         links(string.sub(flag, 3))
     end
+  end
 end
 
 function pkg_config.all(lib)