kernel/os; get rid of a warning when compiling os_msys_init.c when there are no memory pools defined.
kernel/os; get rid of a warning when compiling os_msys_init.c when
there are no memory pools defined.

andrzej-kaczmarek/apache-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,IMGJulian/incubator-mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/apache-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,wes3/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,IMGJulian/incubator-mynewt-core,IMGJulian/incubator-mynewt-core,wes3/incubator-mynewt-core,IMGJulian/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,mlaz/mynewt-core,IMGJulian/incubator-mynewt-core,wes3/incubator-mynewt-core