wscript: Use absolute paths for --libdir, --mandir and --libdir32

wscript

@@ -191,12 +191,12 @@ def configure(conf):
         conf.env['BUILD_JACKD'] = True
 
     if Options.options.libdir:
-        conf.env['LIBDIR'] = conf.env['PREFIX'] + Options.options.libdir
+        conf.env['LIBDIR'] = Options.options.libdir
     else:
         conf.env['LIBDIR'] = conf.env['PREFIX'] + '/lib'
 
     if Options.options.mandir:
-        conf.env['MANDIR'] = conf.env['PREFIX'] + Options.options.mandir
+        conf.env['MANDIR'] = Options.options.mandir
     else:
         conf.env['MANDIR'] = conf.env['PREFIX'] + '/share/man/man1'
 
@@ -239,7 +239,7 @@ def configure(conf):
         conf.env.append_unique('CCFLAGS', '-m32')
         conf.env.append_unique('LINKFLAGS', '-m32')
         if Options.options.libdir32:
-            conf.env['LIBDIR'] = conf.env['PREFIX'] + Options.options.libdir32
+            conf.env['LIBDIR'] = Options.options.libdir32
         else:
             conf.env['LIBDIR'] = conf.env['PREFIX'] + '/lib32'
         conf.write_config_header('config.h')