binfile: ignore vdso bytes if not on Linux

Of course, this all needs improvements to be realistically useful, but
it allows us to get things at least opening. We can adjust how we
store that data to make it available on other OS's later.

src/libsysprof/binfile.c

@@ -300,6 +300,7 @@ get_lines (const char *format,
 static const uint8_t *
 get_vdso_bytes (size_t *length)
 {
+#ifdef __linux__
     static const uint8_t *bytes = NULL;
     static size_t n_bytes = 0;
     static gboolean has_data;
@@ -343,6 +344,11 @@ get_vdso_bytes (size_t *length)
         *length = n_bytes;
 
     return bytes;
+#else
+    if (length)
+        *length = 0;
+    return NULL;
+#endif
 }
 
 bin_file_t *