[vte] build: Fix clang build

[Christian Persch <chpe src gnome org>]

commit a506334ea8148faa7e89eb0a582125391409abe9
Author: Christian Persch <chpe src gnome org>
Date:   Wed Sep 25 12:26:28 2019 +0200

    build: Fix clang build
    
    https://gitlab.gnome.org/GNOME/vte/issues/178

 src/tabstops.hh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/tabstops.hh b/src/tabstops.hh
index 08744f6f..7591318e 100644
--- a/src/tabstops.hh
+++ b/src/tabstops.hh
@@ -32,7 +32,7 @@ public:
         using position_t = unsigned int;
         using signed_position_t = int;
 
-        static position_t const npos = position_t(signed_position_t(-1));
+        static inline constexpr position_t const npos = -1;
 
 private:
         typedef unsigned long storage_t;