Change variable expansion in build scripts

Currently the variable expansion sometimes doesn't work when done over
two variables. Inlining the ~dp0 call along with \..\..\ seems to work.

Testing leads me to believe that the Windows command prompt caches
things in a weird way.

build_scripts/win/package.cmd

@@ -19,9 +19,8 @@ IF NOT DEFINED project_dir (
     REM Arg 0 (called %0) is the full path to the file.
     REM https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/call#batch-parameters
     REM As per above link, %~dp0 expands the zeroth arg to a drive letter and path only.
-    SET folder_path=%~dp0
     REM Project dir is up two dirs from the file.
-    SET project_dir=%folder_path%\..\..\
+    SET project_dir=%~dp0\..\..\
 )
 
 REM ZIP_LOC can't be called 7Z_LOC because of Windows limitations.