Fix definition of predefined ctx and team handles

* Protect casts with parentheses ((type)value) to avoid issues with
  C operator precedence, cf. MPICH and Open MPI mpi.h header file.

include/shmem.h.in.tpl

@@ -88,9 +88,9 @@ typedef void* shmem_team_t;
 typedef struct {
     int num_contexts;
 } shmem_team_config_t;
-#define SHMEM_TEAM_WORLD  (shmem_team_t) 0x90000
-#define SHMEM_TEAM_SHARED (shmem_team_t) 0x90001
-#define SHMEM_TEAM_INVALID NULL
+#define SHMEM_TEAM_WORLD   ((shmem_team_t)0x90000)
+#define SHMEM_TEAM_SHARED  ((shmem_team_t)0x90001)
+#define SHMEM_TEAM_INVALID ((shmem_team_t)NULL)
 
 #define SHMEM_TEAM_NUM_CONTEXTS 0x091001L
 
@@ -104,8 +104,8 @@ typedef struct {
 #define SHMEM_CTX_NOSTORE 0x001003L
 
 typedef void* shmem_ctx_t;
-#define SHMEM_CTX_DEFAULT (shmem_ctx_t) 0x80000
-#define SHMEM_CTX_INVALID NULL
+#define SHMEM_CTX_DEFAULT ((shmem_ctx_t)0x80000)
+#define SHMEM_CTX_INVALID ((shmem_ctx_t)NULL)
 
 /* Signaling Operations */
 #define SHMEM_SIGNAL_SET 0