if inline is not supported check for __inline

This preserves the exisiting behaviour if
config.h_win32vc7 was used.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0a22ac3..ed8c112 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,6 +40,9 @@
 check_type_size("unsigned long long" SIZEOF_UNSIGNED_LONG_LONG)
 
 check_c_source_compiles("inline void func(); void func() { } int main() { func(); return 0; }" HAVE_INLINE)
+if(NOT HAVE_INLINE)
+  check_c_source_compiles("__inline void func(); void func() { } int main() { func(); return 0; }" HAVE___INLINE)
+endif()
 
 set(ENABLE_DEBUG_LOGGING OFF CACHE BOOL "Enable debug logging in all modules")
 set(ERR_REPORTING_STDOUT OFF CACHE BOOL "Enable logging to stdout")