Make eligible global variables static and/or const

For better or worse, Jemalloc has a significant number of global
variables. Making all eligible global variables `static` and/or `const`
at least makes it slightly easier to reason about them, as these
qualifications communicate to the programmer restrictions on their use
without having to `grep` the whole codebase.

include/jemalloc/internal/arena_externs.h

@@ -18,11 +18,10 @@ extern ssize_t opt_dirty_decay_ms;
 extern ssize_t opt_muzzy_decay_ms;
 
 extern percpu_arena_mode_t opt_percpu_arena;
-extern const char *percpu_arena_mode_names[];
+extern const char *const percpu_arena_mode_names[];
 
 extern div_info_t arena_binind_div_info[SC_NBINS];
 
-extern malloc_mutex_t arenas_lock;
 extern emap_t arena_emap_global;
 
 extern size_t opt_oversize_threshold;

include/jemalloc/internal/base.h

@@ -23,7 +23,7 @@ typedef enum metadata_thp_mode_e metadata_thp_mode_t;
 
 #define METADATA_THP_DEFAULT metadata_thp_disabled
 extern metadata_thp_mode_t opt_metadata_thp;
-extern const char *metadata_thp_mode_names[];
+extern const char *const metadata_thp_mode_names[];
 
 
 /* Embedded at the beginning of every block of base-managed virtual memory. */

include/jemalloc/internal/extent_dss.h

@@ -11,7 +11,7 @@ typedef enum {
 #define DSS_PREC_DEFAULT dss_prec_secondary
 #define DSS_DEFAULT "secondary"
 
-extern const char *dss_prec_names[];
+extern const char *const dss_prec_names[];
 
 extern const char *opt_dss;
 

include/jemalloc/internal/hpa_hooks.h

@@ -12,6 +12,6 @@ struct hpa_hooks_s {
 	uint64_t (*ms_since)(nstime_t *r_time);
 };
 
-extern hpa_hooks_t hpa_hooks_default;
+extern const hpa_hooks_t hpa_hooks_default;
 
 #endif /* JEMALLOC_INTERNAL_HPA_HOOKS_H */

include/jemalloc/internal/jemalloc_internal_externs.h

@@ -22,8 +22,8 @@ extern sec_opts_t opt_hpa_sec_opts;
 extern const char *opt_junk;
 extern bool opt_junk_alloc;
 extern bool opt_junk_free;
-extern void (*junk_free_callback)(void *ptr, size_t size);
-extern void (*junk_alloc_callback)(void *ptr, size_t size);
+extern void (*JET_MUTABLE junk_free_callback)(void *ptr, size_t size);
+extern void (*JET_MUTABLE junk_alloc_callback)(void *ptr, size_t size);
 extern bool opt_utrace;
 extern bool opt_xmalloc;
 extern bool opt_experimental_infallible_new;
@@ -31,7 +31,7 @@ extern bool opt_zero;
 extern unsigned opt_narenas;
 extern zero_realloc_action_t opt_zero_realloc_action;
 extern malloc_init_t malloc_init_state;
-extern const char *zero_realloc_mode_names[];
+extern const char *const zero_realloc_mode_names[];
 extern atomic_zu_t zero_realloc_count;
 extern bool opt_cache_oblivious;
 extern unsigned opt_debug_double_free_max_scan;

include/jemalloc/internal/nstime.h

@@ -56,7 +56,7 @@ enum prof_time_res_e {
 typedef enum prof_time_res_e prof_time_res_t;
 
 extern prof_time_res_t opt_prof_time_res;
-extern const char *prof_time_res_mode_names[];
+extern const char *const prof_time_res_mode_names[];
 
 JEMALLOC_ALWAYS_INLINE void
 nstime_init_zero(nstime_t *time) {

include/jemalloc/internal/pa.h

@@ -131,7 +131,7 @@ pa_shard_ehooks_get(pa_shard_t *shard) {
 
 /* Returns true on error. */
 bool pa_central_init(pa_central_t *central, base_t *base, bool hpa,
-    hpa_hooks_t *hpa_hooks);
+    const hpa_hooks_t *hpa_hooks);
 
 /* Returns true on error. */
 bool pa_shard_init(tsdn_t *tsdn, pa_shard_t *shard, pa_central_t *central,

include/jemalloc/internal/pages.h

@@ -102,7 +102,7 @@ typedef enum {
 #define THP_MODE_DEFAULT thp_mode_default
 extern thp_mode_t opt_thp;
 extern thp_mode_t init_system_thp_mode; /* Initial system wide state. */
-extern const char *thp_mode_names[];
+extern const char *const thp_mode_names[];
 
 void *pages_map(void *addr, size_t size, size_t alignment, bool *commit);
 void pages_unmap(void *addr, size_t size);