scons: Cleanup flex/bison settings specification.

Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/src/mesa/SConscript b/src/mesa/SConscript
index 72d9811..a563fd2 100644
--- a/src/mesa/SConscript
+++ b/src/mesa/SConscript
@@ -39,7 +39,7 @@
 # parse Makefile.sources
 source_lists = env.ParseSourceList('Makefile.sources')
 
-env.Append(YACCFLAGS = '-d -p "_mesa_program_"')
+env.Append(YACCFLAGS = ['-d', '-p', '_mesa_program_'])
 env.CFile('program/lex.yy.c', 'program/program_lexer.l')
 env.CFile('program/program_parse.tab.c', 'program/program_parse.y')