Use atexit() only if it's safe to call from shared library

Apparently they are not (advertised as?) safe on BSD systems.
We ignore the case of static libraries.

Whitelisted on glibc, Android, and MSVC / mingw.

https://bugs.freedesktop.org/show_bug.cgi?id=82246

src/hb-common.cc

@@ -234,7 +234,7 @@ struct hb_language_item_t {
 
 static hb_language_item_t *langs;
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
 static inline
 void free_langs (void)
 {
@@ -269,7 +269,7 @@ retry:
     goto retry;
   }
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
   if (!first_lang)
     atexit (free_langs); /* First person registers atexit() callback. */
 #endif

src/hb-ft.cc

@@ -455,7 +455,7 @@ retry:
       goto retry;
     }
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
     atexit (free_ft_library); /* First person registers atexit() callback. */
 #endif
   }

src/hb-private.hh

@@ -130,6 +130,31 @@
 #  define STRICT
 #endif
 
+#if HAVE_ATEXIT
+/* atexit() is only safe to be called from shared libraries on certain
+ * platforms.  Whitelist.
+ * https://bugs.freedesktop.org/show_bug.cgi?id=82246 */
+#  if defined(__linux) && defined(__GLIBC_PREREQ)
+#    if __GLIBC_PREREQ(2,3)
+/* From atexit() manpage, it's safe with glibc 2.2.3 on Linux. */
+#      define HB_USE_ATEXIT 1
+#    endif
+#  elif defined(_MSC_VER) || defined(__MINGW32__)
+/* For MSVC:
+ * http://msdn.microsoft.com/en-ca/library/tze57ck3.aspx
+ * http://msdn.microsoft.com/en-ca/library/zk17ww08.aspx
+ * mingw32 headers say atexit is safe to use in shared libraries.
+ */
+#    define HB_USE_ATEXIT 1
+#  elif defined(__ANDROID__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))
+/* This was fixed in Android NKD r8 or r8b:
+ * https://code.google.com/p/android/issues/detail?id=6455
+ * which introduced GCC 4.6:
+ * https://developer.android.com/tools/sdk/ndk/index.html
+ */
+#    define HB_USE_ATEXIT 1
+#  endif
+#endif
 
 /* Basics */
 

src/hb-shape.cc

@@ -320,7 +320,7 @@ retry:
       goto retry;
     }
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
     atexit (free_static_shaper_list); /* First person registers atexit() callback. */
 #endif
   }

src/hb-shaper.cc

@@ -100,7 +100,7 @@ retry:
       goto retry;
     }
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
     atexit (free_static_shapers); /* First person registers atexit() callback. */
 #endif
   }

src/hb-uniscribe.cc

@@ -245,7 +245,7 @@ retry:
       goto retry;
     }
 
-#ifdef HAVE_ATEXIT
+#ifdef HB_USE_ATEXIT
     atexit (free_uniscribe_funcs); /* First person registers atexit() callback. */
 #endif
   }