setup cc flags in lex_yacc_target

N/A

Include paths introduced by the 'export_incs' property of lex_yacc_target's
dependencies are not added while compiling the c source code generated from lex
yacc source. This change will fix it.

Change-Id: I3aef7be0cd556b296ebf173156b9a25427551643
Signed-off-by: liuhuahang <liuhuahang@zerus.co>
Merge pull request #112 from huahang/patch

setup cc flags in lex_yacc_target