bi: Use Boost.Predef to detect and expose the build arch

This commit also adds this information to the startup banner on stderr,
the output of --report, and the Game Version dialog's main UI and
clipboard report.

src/build_info.cpp

@@ -38,6 +38,7 @@
 #include <SDL2/SDL_ttf.h>
 
 #include <boost/algorithm/string.hpp>
+#include <boost/predef.h>
 #include <boost/version.hpp>
 
 #ifndef __APPLE__
@@ -309,6 +310,39 @@ const std::string empty_version = "";
 
 } // end anonymous namespace 1
 
+std::string build_arch()
+{
+#if BOOST_ARCH_X86_64
+	return "x86_64";
+#elif BOOST_ARCH_X86_32
+	return "x86";
+#elif BOOST_ARCH_ARM && (defined(__arm64) || defined(_M_ARM64))
+	return "arm64";
+#elif BOOST_ARCH_ARM
+	return "arm";
+#elif BOOST_ARCH_IA64
+	return "ia64";
+#elif BOOST_ARCH_PPC
+	return "ppc";
+#elif BOOST_ARCH_ALPHA
+	return "alpha";
+#elif BOOST_ARCH_MIPS
+	return "mips";
+#elif BOOST_ARCH_SPARC
+	return "sparc";
+#else
+	// Congratulations, you're running Wesnoth on an exotic platform -- either that or you live in
+	// the foretold future where x86 and ARM stopped being the dominant CPU architectures for the
+	// general-purpose consumer market. If you want to add label support for your platform, check
+	// out the Boost.Predef library's documentation and alter the code above accordingly.
+	//
+	// On the other hand, if you got here looking for Wesnoth's biggest secret let me just say
+	// right here and now that Irdya is round. There, I said the thing that nobody has dared say
+	// in mainline content before.
+	return _("cpu_architecture^<unknown>");
+#endif
+}
+
 std::vector<optional_feature> optional_features_table()
 {
 	std::vector<optional_feature> res = versions.features;
@@ -637,7 +671,7 @@ std::string full_build_report()
 
 	std::ostringstream o;
 
-	o << "The Battle for Wesnoth version " << game_config::revision << '\n'
+	o << "The Battle for Wesnoth version " << game_config::revision << " " << build_arch() << '\n'
 	  << "Running on " << desktop::os_version() << '\n'
 	  << "Distribution channel: " << dist_channel_id() << '\n'
 	  << '\n'

src/build_info.hpp

@@ -46,6 +46,11 @@ struct optional_feature
 	optional_feature(const char* n) : name(n), enabled(false) {}
 };
 
+/**
+ * Obtain the processor architecture for this build.
+ */
+std::string build_arch();
+
 /**
  * Return a localized features table.
  */

src/gui/dialogs/game_version_dialog.cpp

@@ -102,7 +102,7 @@ void game_version::pre_show(window& window)
 	//
 
 	styled_widget& version_label = find_widget<styled_widget>(&window, "version", false);
-	i18n_syms["version"] = game_config::revision;
+	i18n_syms["version"] = game_config::revision + " " + game_config::build_arch();
 	version_label.set_label(VGETTEXT("Version $version", i18n_syms));
 
 	styled_widget& os_label = find_widget<styled_widget>(&window, "os", false);

src/wesnoth.cpp

@@ -1026,7 +1026,7 @@ int main(int argc, char** argv)
 	SDL_StartTextInput();
 
 	try {
-		std::cerr << "Battle for Wesnoth v" << game_config::revision << '\n';
+		std::cerr << "Battle for Wesnoth v" << game_config::revision  << " " << game_config::build_arch() << '\n';
 		const std::time_t t = std::time(nullptr);
 		std::cerr << "Started on " << ctime(&t) << "\n";