oid: move thread local storage into oid.c

Now that thread-local error data is handled in error, move the thread
local data out of the `threadstate` object, since it has now become
useless indirection.

src/libgit2/libgit2.c

@@ -76,6 +76,7 @@ int git_libgit2_init(void)
 		git_error_global_init,
 		git_threadstate_global_init,
 		git_threads_global_init,
+		git_oid_global_init,
 		git_rand_global_init,
 		git_hash_global_init,
 		git_sysdir_global_init,

src/libgit2/oid.c

@@ -9,7 +9,7 @@
 
 #include "git2/oid.h"
 #include "repository.h"
-#include "threadstate.h"
+#include "runtime.h"
 #include <string.h>
 #include <limits.h>
 
@@ -153,15 +153,42 @@ int git_oid_pathfmt(char *str, const git_oid *oid)
 	return 0;
 }
 
+static git_tlsdata_key thread_str_key;
+
+static void GIT_SYSTEM_CALL thread_str_free(void *s)
+{
+	char *str = (char *)s;
+	git__free(str);
+}
+
+static void thread_str_global_shutdown(void)
+{
+	char *str = git_tlsdata_get(thread_str_key);
+	git_tlsdata_set(thread_str_key, NULL);
+
+	git__free(str);
+	git_tlsdata_dispose(thread_str_key);
+}
+
+int git_oid_global_init(void)
+{
+	if (git_tlsdata_init(&thread_str_key, thread_str_free) != 0)
+		return -1;
+
+	return git_runtime_shutdown_register(thread_str_global_shutdown);
+}
+
 char *git_oid_tostr_s(const git_oid *oid)
 {
-	git_threadstate *threadstate = git_threadstate_get();
 	char *str;
 
-	if (!threadstate)
-		return NULL;
+	if ((str = git_tlsdata_get(thread_str_key)) == NULL) {
+		if ((str = git__malloc(GIT_OID_MAX_HEXSIZE + 1)) == NULL)
+			return NULL;
+
+		git_tlsdata_set(thread_str_key, str);
+	}
 
-	str = threadstate->oid_fmt;
 	git_oid_nfmt(str, git_oid_hexsize(git_oid_type(oid)) + 1, oid);
 	return str;
 }

src/libgit2/oid.h

@@ -270,4 +270,6 @@ int git_oid__fromstrn(
 
 int git_oid__fromraw(git_oid *out, const unsigned char *raw, git_oid_t type);
 
+int git_oid_global_init(void);
+
 #endif