-Werror,-Wunused-macros

Whatever those _POSIX_ for _MSV_VER were supposed to be good for (have been in
there at least ever since 4f4b7415 "Moved cpp
from cpp to soltools"), but cause -Wunused-macros at least when building with
clang-cl.

Change-Id: I356bf663cd1e86298ba72a179f46bb9d0c10016b

soltools/cpp/_include.c

@@ -23,9 +23,6 @@
 #   include <unistd.h>
 #endif
 
-#ifdef _MSC_VER
-#   define _POSIX_
-#endif
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

soltools/cpp/_macro.c

@@ -17,9 +17,6 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
-#ifdef _MSC_VER
-#   define _POSIX_
-#endif
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>