[glib: 1/2] build: Fix ssize_t detection on older versions of glibc

[Sebastian Dröge <sdroege src gnome org>]

commit 6837c81d0e0f1cc6467ee850fdff0c62d8a95d56
Author: Ole André Vadla Ravnås <oleavr gmail com>
Date:   Sun Nov 15 00:37:19 2020 +0000

    build: Fix ssize_t detection on older versions of glibc

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 05dfff027..8832ff04f 100644
--- a/meson.build
+++ b/meson.build
@@ -1273,7 +1273,7 @@ sizet_size = cc.sizeof('size_t')
 if cc.get_id() == 'msvc' or cc.get_id() == 'clang-cl'
   ssizet_size = cc.sizeof('SSIZE_T', prefix : '#include <BaseTsd.h>')
 else
-  ssizet_size = cc.sizeof('ssize_t')
+  ssizet_size = cc.sizeof('ssize_t', prefix : '#include <unistd.h>')
 endif
 
 # Some platforms (Apple) hard-code int64_t to long long instead of