Check availability of constructor attribute and use it on Windows in …

…favor of DllMain

configure.ac

@@ -73,6 +73,24 @@ case ${host_os} in
 esac
 AM_CONDITIONAL(WIN32, test x$win32 = xtrue)
 
+# Check if the C compiler supports __attribute__((constructor))
+AC_CACHE_CHECK([wether the C compiler supports constructor/destructor attributes],
+  ac_cv_attribute_constructor, [
+  ac_cv_attribute_constructor=no
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+    [[
+      static void __attribute__((constructor)) test_constructor(void) {
+      }
+      static void __attribute__((destructor)) test_destructor(void) {
+      }
+    ]], [])],
+    [ac_cv_attribute_constructor=yes]
+  )]
+)
+if test "$ac_cv_attribute_constructor" = "yes"; then
+  AC_DEFINE(HAVE_ATTRIBUTE_CONSTRUCTOR, 1, [Define if the C compiler supports constructor/destructor attributes])
+fi
+
 AS_COMPILER_FLAGS(GLOBAL_CFLAGS, "-Wall -Wextra -Wmissing-declarations -Wredundant-decls -Wshadow -Wpointer-arith  -Wwrite-strings -Wswitch-default -Wno-unused-parameter -fsigned-char -fvisibility=hidden")
 AC_SUBST(GLOBAL_CFLAGS)
 

src/activation.c

@@ -101,7 +101,6 @@ static void internal_libideviceactivation_deinit(void)
 }
 
 #ifdef WIN32
-
 typedef volatile struct {
     LONG lock;
     int state;
@@ -121,7 +120,29 @@ static void thread_once(thread_once_t *once_control, void (*init_routine)(void))
     }
     InterlockedExchange(&(once_control->lock), 0);
 }
+#else
+static pthread_once_t init_once = PTHREAD_ONCE_INIT;
+static pthread_once_t deinit_once = PTHREAD_ONCE_INIT;
+#define thread_once pthread_once
+#endif
+
+#ifndef HAVE_ATTRIBUTE_CONSTRUCTOR
+  #if defined(__llvm__) || defined(__GNUC__)
+    #define HAVE_ATTRIBUTE_CONSTRUCTOR
+  #endif
+#endif
+
+#ifdef HAVE_ATTRIBUTE_CONSTRUCTOR
+static void __attribute__((constructor)) libideviceactivation_initialize(void)
+{
+    thread_once(&init_once, internal_libideviceactivation_init);
+}
 
+static void __attribute__((destructor)) libideviceactivation_deinitialize(void)
+{
+    thread_once(&deinit_once, internal_libideviceactivation_deinit);
+}
+#elif defined(WIN32)
 BOOL WINAPI DllMain(HINSTANCE hModule, DWORD dwReason, LPVOID lpReserved)
 {
     switch (dwReason) {
@@ -136,25 +157,10 @@ BOOL WINAPI DllMain(HINSTANCE hModule, DWORD dwReason, LPVOID lpReserved)
     }
     return 1;
 }
-
 #else
-
-static pthread_once_t init_once = PTHREAD_ONCE_INIT;
-static pthread_once_t deinit_once = PTHREAD_ONCE_INIT;
-
-static void __attribute__((constructor)) libideviceactivation_initialize(void)
-{
-    pthread_once(&init_once, internal_libideviceactivation_init);
-}
-
-static void __attribute__((destructor)) libideviceactivation_deinitialize(void)
-{
-    pthread_once(&deinit_once, internal_libideviceactivation_deinit);
-}
-
+#warning No compiler support for constructor/destructor attributes, some features might not be available.
 #endif
 
-
 static int debug_level = 0;
 
 IDEVICE_ACTIVATION_API void idevice_activation_set_debug_level(int level) {