libjpeg: force HAVE_BOOLEAN

to avoid conflicts like:
.../spksrc/cross/leptonica/work-evansport/install//usr/local/include/jmorecfg.h:263:16: error: expected identifier before numeric constant
make[5]: *** [tif_jpeg.lo] Error 1

Because in other libraries (libtiff and giflib in my case) is TRUE,FALSE defined as constants.
Using HAVE_BOOLEAN forces libjpeg to use it as constants too.

P.S.: I'm not really sure if it is a clean solution, but I don't know how to do better. So this is something between "pull request" and "issue".