Make eligible functions static

The codebase is already very disciplined in making any function which
can be `static`, but there are a few that appear to have slipped through
the cracks.

src/decay.c

@@ -14,7 +14,7 @@ static const uint64_t h_steps[SMOOTHSTEP_NSTEPS] = {
  * Generate a new deadline that is uniformly random within the next epoch after
  * the current one.
  */
-void
+static void
 decay_deadline_init(decay_t *decay) {
 	nstime_copy(&decay->deadline, &decay->epoch);
 	nstime_add(&decay->deadline, &decay->interval);

src/extent.c

@@ -43,6 +43,8 @@ static edata_t *extent_try_coalesce(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
 static edata_t *extent_alloc_retained(tsdn_t *tsdn, pac_t *pac,
     ehooks_t *ehooks, edata_t *expand_edata, size_t size, size_t alignment,
     bool zero, bool *commit, bool guarded);
+static bool extent_decommit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks,
+    edata_t *edata, size_t offset, size_t length);
 
 /******************************************************************************/
 
@@ -1118,7 +1120,7 @@ extent_commit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
 	    /* growing_retained */ false);
 }
 
-bool
+static bool
 extent_decommit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
     size_t offset, size_t length) {
 	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),

src/hpa.c

@@ -83,7 +83,7 @@ hpa_alloc_ps(tsdn_t *tsdn, hpa_central_t *central) {
 	    CACHELINE);
 }
 
-hpdata_t *
+static hpdata_t *
 hpa_central_extract(tsdn_t *tsdn, hpa_central_t *central, size_t size,
     bool *oom) {
 	/* Don't yet support big allocations; these should get filtered out. */