fix: ensure export macro to be defined (#1031)

src/glog/flags.h

@@ -41,6 +41,10 @@
 #  include "glog/export.h"
 #endif
 
+#if !defined(GLOG_EXPORT)
+#  error <glog/flags.h> was not included correctly. See the documention for how to consume the library.
+#endif
+
 #include "glog/platform.h"
 #include "glog/types.h"
 

src/glog/log_severity.h

@@ -34,6 +34,10 @@
 #  include "glog/export.h"
 #endif
 
+#if !defined(GLOG_EXPORT)
+#  error <glog/log_severity.h> was not included correctly. See the documention for how to consume the library.
+#endif
+
 namespace google {
 
 // The recommended semantics of the log levels are as follows:

src/glog/logging.h

@@ -56,6 +56,10 @@
 #  include "glog/export.h"
 #endif
 
+#if !defined(GLOG_EXPORT)
+#  error <glog/logging.h> was not included correctly. See the documention for how to consume the library.
+#endif
+
 #include "glog/flags.h"
 #include "glog/platform.h"
 #include "glog/types.h"

src/glog/raw_logging.h

@@ -36,13 +36,17 @@
 #ifndef GLOG_RAW_LOGGING_H
 #define GLOG_RAW_LOGGING_H
 
-#include "glog/log_severity.h"
-#include "glog/vlog_is_on.h"
-
 #if defined(GLOG_USE_GLOG_EXPORT)
 #  include "glog/export.h"
 #endif
 
+#if !defined(GLOG_EXPORT)
+#  error <glog/raw_logging.h> was not included correctly. See the documention for how to consume the library.
+#endif
+
+#include "glog/log_severity.h"
+#include "glog/vlog_is_on.h"
+
 namespace google {
 
 // This is similar to LOG(severity) << format... and VLOG(level) << format..,

src/glog/vlog_is_on.h

@@ -67,6 +67,10 @@
 #  include "glog/export.h"
 #endif
 
+#if !defined(GLOG_EXPORT)
+#  error <glog/vlog_is_on.h> was not included correctly. See the documention for how to consume the library.
+#endif
+
 #include "glog/flags.h"
 #include "glog/types.h"