setools: fix race condition

As reported upstream:

  https://github.com/TresysTechnology/setools3/issues/5

setools tries to compile a .c file before being generated and then it
produces an error like this one:

error: policy_scan.c: No such file or directory

Until upstream fixes the problem we can workaround this by using MAKE1
as the SETOOLS_MAKE.

Fixes:

  http://autobuild.buildroot.net/results/119/1196ac448c77320b59b63b6133d2d1af1245bf69/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>