libmysqlclient: fix x86_64 shared build and add test program

see #914, I'm not sure why the `def` file is needed on i686 shared.

src/libmysqlclient-test.c

@@ -0,0 +1,23 @@
+/*
+ * This file is part of MXE.
+ * See index.html for further information.
+ */
+
+#include <mysql.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+    (void)argc;
+    (void)argv;
+
+    if (mysql_library_init(0, NULL, NULL)) {
+        fprintf(stderr, "Could not initialize MySQL library\n");
+        exit(1);
+    }
+
+    printf("MySQL client library initialized: %s\n", mysql_get_client_info());
+    mysql_library_end();
+
+    return EXIT_SUCCESS;
+}

src/libmysqlclient.mk

@@ -36,7 +36,8 @@ define $(PKG)_BUILD
         '$(1)'
 
     # def file created by cmake creates link errors
-    cp '$(PWD)/src/$(PKG).def' '$(1).build/libmysql/libmysql_exports.def'
+    $(if $(findstring i686-w64-mingw32.shared,$(TARGET)),
+        cp '$(PWD)/src/$(PKG).def' '$(1).build/libmysql/libmysql_exports.def')
 
     $(MAKE) -C '$(1).build' -j '$(JOBS)' VERBOSE=1
     $(MAKE) -C '$(1).build/include'  -j 1 install VERBOSE=1
@@ -48,4 +49,10 @@ define $(PKG)_BUILD
 
     # missing headers
     $(INSTALL) -m644 '$(1)/include/'thr_* '$(1)/include/'my_thr* '$(PREFIX)/$(TARGET)/include'
+
+    # build test with mysql_config
+    '$(TARGET)-g++' \
+        -W -Wall -Werror -ansi -pedantic \
+        '$(2).c' -o '$(PREFIX)/$(TARGET)/bin/test-$(PKG).exe' \
+        `'$(PREFIX)/$(TARGET)/bin/mysql_config' --cflags --libs`
 endef