Link to DbgHelp using pre-processor directive

This method ensure that all users of glog get automatically linked to
the DbgHelp library without needing to set compiler flags.

CMakeLists.txt

@@ -458,7 +458,6 @@ endif (HAVE_EXECINFO_H)
 if (WIN32)
   set (HAVE_STACKTRACE 1)
   set (HAVE_SYMBOLIZE 1)
-  target_link_libraries (glog PUBLIC Dbghelp.lib)
 endif (WIN32)
 
 if (UNIX OR (APPLE AND HAVE_DLADDR))

src/demangle.cc

@@ -40,6 +40,7 @@
 
 #if defined(OS_WINDOWS)
 #include <DbgHelp.h>
+#pragma comment(lib, "DbgHelp")
 #endif
 
 _START_GOOGLE_NAMESPACE_

src/symbolize.cc

@@ -840,6 +840,7 @@ _END_GOOGLE_NAMESPACE_
 #elif defined(OS_WINDOWS)
 
 #include <DbgHelp.h>
+#pragma comment(lib, "DbgHelp")
 
 _START_GOOGLE_NAMESPACE_