Break up headers into constituent parts

This is part of a broader change to make header files better represent the
dependencies between one another (see
https://github.com/jemalloc/jemalloc/issues/533). It breaks up component headers
into smaller parts that can be made to have a simpler dependency graph.

For the autogenerated headers (smoothstep.h and size_classes.h), no splitting
was necessary, so I didn't add support to emit multiple headers.

include/jemalloc/internal/tcache_structs.h

@@ -0,0 +1,55 @@
+#ifndef JEMALLOC_INTERNAL_TCACHE_STRUCTS_H
+#define JEMALLOC_INTERNAL_TCACHE_STRUCTS_H
+
+typedef enum {
+	tcache_enabled_false   = 0, /* Enable cast to/from bool. */
+	tcache_enabled_true    = 1,
+	tcache_enabled_default = 2
+} tcache_enabled_t;
+
+/*
+ * Read-only information associated with each element of tcache_t's tbins array
+ * is stored separately, mainly to reduce memory usage.
+ */
+struct tcache_bin_info_s {
+	unsigned	ncached_max;	/* Upper limit on ncached. */
+};
+
+struct tcache_bin_s {
+	tcache_bin_stats_t tstats;
+	int		low_water;	/* Min # cached since last GC. */
+	unsigned	lg_fill_div;	/* Fill (ncached_max >> lg_fill_div). */
+	unsigned	ncached;	/* # of cached objects. */
+	/*
+	 * To make use of adjacent cacheline prefetch, the items in the avail
+	 * stack goes to higher address for newer allocations.  avail points
+	 * just above the available space, which means that
+	 * avail[-ncached, ... -1] are available items and the lowest item will
+	 * be allocated first.
+	 */
+	void		**avail;	/* Stack of available objects. */
+};
+
+struct tcache_s {
+	ql_elm(tcache_t) link;		/* Used for aggregating stats. */
+	uint64_t	prof_accumbytes;/* Cleared after arena_prof_accum(). */
+	ticker_t	gc_ticker;	/* Drives incremental GC. */
+	szind_t		next_gc_bin;	/* Next bin to GC. */
+	tcache_bin_t	tbins[1];	/* Dynamically sized. */
+	/*
+	 * The pointer stacks associated with tbins follow as a contiguous
+	 * array.  During tcache initialization, the avail pointer in each
+	 * element of tbins is initialized to point to the proper offset within
+	 * this array.
+	 */
+};
+
+/* Linkage for list of available (previously used) explicit tcache IDs. */
+struct tcaches_s {
+	union {
+		tcache_t	*tcache;
+		tcaches_t	*next;
+	};
+};
+
+#endif /* JEMALLOC_INTERNAL_TCACHE_STRUCTS_H */