Use alternative name for internal expat_config.h

Avoid clashes when system has expat installed.

3rdparty/expat/CMakeLists.txt

@@ -1,7 +1,7 @@
 
 configure_file (
     "${PROJECT_SOURCE_DIR}/3rdparty/expat/expat_config_cmake.in"
-    "${PROJECT_BINARY_DIR}/3rdparty/expat/expat_config.h"
+    "${PROJECT_BINARY_DIR}/3rdparty/expat/simgear_expat_config.h"
 )
 
 set(expat_sources 

3rdparty/expat/xmlparse.c

@@ -18,6 +18,8 @@
 #include "amigaconfig.h"
 #elif defined(__WATCOMC__)
 #include "watcomconfig.h"
+#elif defined(HAVE_SIMGEAR_EXPAT_CONFIG_H)
+#include "simgear_expat_config.h"
 #elif defined(HAVE_EXPAT_CONFIG_H)
 #include "expat_config.h"
 #endif /* ndef COMPILED_FROM_DSP */

3rdparty/expat/xmlrole.c

@@ -12,6 +12,8 @@
 #include "amigaconfig.h"
 #elif defined(__WATCOMC__)
 #include "watcomconfig.h"
+#elif defined(HAVE_SIMGEAR_EXPAT_CONFIG_H)
+#include "simgear_expat_config.h"
 #else
 #ifdef HAVE_EXPAT_CONFIG_H
 #include "expat_config.h"

3rdparty/expat/xmltok.c

@@ -12,6 +12,8 @@
 #include "amigaconfig.h"
 #elif defined(__WATCOMC__)
 #include "watcomconfig.h"
+#elif defined(HAVE_SIMGEAR_EXPAT_CONFIG_H)
+#include "simgear_expat_config.h"
 #else
 #ifdef HAVE_EXPAT_CONFIG_H
 #include "expat_config.h"