[libglnx] glnx_strjoina: Cast to result for C++ compatibility

[Colin Walters <walters src gnome org>]

commit a8b4418954bf200746dc5c5cc450649cc345cbd2
Author: Colin Walters <walters verbum org>
Date:   Sun Nov 22 22:59:45 2020 +0000

    glnx_strjoina: Cast to result for C++ compatibility
    
    Prep for using C++ in rpm-ostree (temporarily).

 glnx-macros.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/glnx-macros.h b/glnx-macros.h
index 700fc75..7b3afd4 100644
--- a/glnx-macros.h
+++ b/glnx-macros.h
@@ -52,7 +52,7 @@ G_BEGIN_DECLS
                 unsigned _i_;                                           \
                 for (_i_ = 0; _i_ < G_N_ELEMENTS(_appendees_) && _appendees_[_i_]; _i_++) \
                         _len_ += strlen(_appendees_[_i_]);              \
-                _p_ = _d_ = alloca(_len_ + 1);                          \
+                _p_ = _d_ = (char*) alloca(_len_ + 1);                          \
                 for (_i_ = 0; _i_ < G_N_ELEMENTS(_appendees_) && _appendees_[_i_]; _i_++) \
                         _p_ = stpcpy(_p_, _appendees_[_i_]);            \
                 *_p_ = 0;                                               \