Fixup freedren bison/lex usage

All the calls to bison and flex were duplicated.

The bison calls were missing the M4 env variable
causing the usage of m4 from $PATH instead of prebuilts.

Seems like mesa had already in place a way to make
use use proper calls to flex, we augment that to also
support bison ( depending Android version )

Change-Id: Ibe4e9224b23c7574975df1c7101c69581bc353b4
2 files changed