sqlite3: Implement some auxiliary functions

This adds `sqlite3_libversion()`, `sqlite3_libversion_number()`, and
`libsql3_threadsafe()`.

sqlite3/src/lib.rs

@@ -773,15 +773,17 @@ pub unsafe extern "C" fn sqlite3_complete(_sql: *const std::ffi::c_char) -> ffi:
 
 #[no_mangle]
 pub unsafe extern "C" fn sqlite3_threadsafe() -> ffi::c_int {
-    todo!();
+    1
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn sqlite3_libversion() -> *const std::ffi::c_char {
-    todo!();
+    ffi::CStr::from_bytes_with_nul(b"3.42.0\0")
+        .unwrap()
+        .as_ptr()
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn sqlite3_libversion_number() -> ffi::c_int {
-    todo!();
+    3042000
 }

sqlite3/tests/Makefile

@@ -15,6 +15,7 @@ CFLAGS = -g -Wall -std=c17 -MMD -MP
 LIBS ?= -lsqlite3
 
 OBJS += main.o
+OBJS += test-aux.o
 OBJS += test-close.o
 OBJS += test-open.o
 OBJS += test-prepare.o

sqlite3/tests/main.c

@@ -1,3 +1,5 @@
+extern void test_libversion();
+extern void test_libversion_number();
 extern void test_open_misuse();
 extern void test_open_not_found();
 extern void test_open_existing();
@@ -6,6 +8,8 @@ extern void test_prepare_misuse();
 
 int main(int argc, char *argv[])
 {
+	test_libversion();
+	test_libversion_number();
 	test_open_misuse();
 	test_open_not_found();
 	test_open_existing();

sqlite3/tests/test-aux.c

@@ -0,0 +1,11 @@
+#include "check.h"
+
+#include <sqlite3.h>
+
+void test_libversion(void) {
+    sqlite3_libversion();
+}
+
+void test_libversion_number(void) {
+  sqlite3_libversion_number();
+}