Make: remove -e from subdirectory command

in gmake, -e gives precedence to variables defined in the environment.
this argument disables appending to CFLAGS or CXXFLAGS when they are set
in the environment and breaks our make configuration.

Change-Id: Id395e7edc4b243bd3805d7f5fdb3456d94893952
Signed-off-by: Seth Howell <seth.howell@intel.com>
Reviewed-on: https://review.gerrithub.io/400863


Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>