Mark two public functions ZIP_EXTERN.

lib/zip_source_stat.c

diff --git a/lib/zip_source_stat.c b/lib/zip_source_stat.c
index 34cb05f..4f08d42 100644
--- a/lib/zip_source_stat.c
+++ b/lib/zip_source_stat.c
@@ -35,7 +35,7 @@
 #include "zipint.h"
 
 
-int
+ZIP_EXTERN int
 zip_source_stat(zip_source_t *src, zip_stat_t *st)
 {
     if (src->source_closed) {

lib/zip_source_supports.c

diff --git a/lib/zip_source_supports.c b/lib/zip_source_supports.c
index 3c100fb..2179037 100644
--- a/lib/zip_source_supports.c
+++ b/lib/zip_source_supports.c
@@ -44,7 +44,7 @@
 }
 
 
-zip_int64_t
+ZIP_EXTERN zip_int64_t
 zip_source_make_command_bitmap(zip_source_cmd_t cmd0, ...)
 {
     zip_int64_t bitmap;