Write NB_ANTENNAS_RX/TX to header file and use in stack

Prior to this commit, constants NB_ANTENNAS_RX/TX are provided on the
command line to each compiler invocation. This has the drawback (1) that
also files that don't need that get the constants, and (2) it is not
easy to find them using ctags or similar, as the only definition is in
CMakeLists.txt (where it is not found).

In this commit, use cmake configure_file() to write a header file with
these constants. The file will be generated during cmake invocation, and
written to <build-dir>/common/cmake_defs.h. The relevant files that
need this definition will pick it from the header.

This has been used previously also in a commit to write git information.

See-also: 8bffd1666d ("Avoid complete rebuild on cmake run with git info change")

radio/COMMON/common_lib.h

@@ -35,6 +35,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <sys/types.h>
+#include "common/cmake_defs.h"
 #include <openair1/PHY/TOOLS/tools_defs.h>
 #include "record_player.h"
 #include "common/utils/threadPool/notified_fifo.h"