Fix build under Visual Studio 2017

Add a few defines and make 'main' functions extern "C" (see SDL_main.h)
to fix the build under Visual Studio 2017.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

CMakeLists.txt

@@ -23,6 +23,14 @@ if (WIN32)
 	set(CMAKE_INSTALL_BINDIR ${CMAKE_INSTALL_PREFIX})
 endif (WIN32)
 
+if (MSVC)
+	# Avoid annoying warnings from Visual Studio
+	add_definitions(-D_CRT_SECURE_NO_WARNINGS)
+
+	# Use M_PI/M_E macros from math.h
+	add_definitions(-D_USE_MATH_DEFINES -DHAVE_M_PI)
+endif (MSVC)
+
 if (APPLE)
 	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-gnu")
 	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-gnu")
@@ -171,6 +179,10 @@ if (NOT USE_SYSTEM_LIBGLEW)
 	add_subdirectory(contrib/glew)
 	add_library(GLEW::GLEW ALIAS glew)
 	include_directories(contrib/glew)
+
+	# Specify that we compile against a static build of Glew
+	# (required on Windows)
+	add_definitions(-DGLEW_STATIC)
 endif (NOT USE_SYSTEM_LIBGLEW)
 add_subdirectory(contrib/imgui)
 add_subdirectory(contrib/jenkins)

src/main.cpp

@@ -23,7 +23,7 @@ enum RunMode {
 	MODE_USAGE_ERROR
 };
 
-int main(int argc, char **argv)
+extern "C" int main(int argc, char **argv)
 {
 #ifdef PIONEER_PROFILER
 	Profiler::detect(argc, argv);

src/modelcompiler.cpp

@@ -158,7 +158,7 @@ enum RunMode {
 
 static FileSystem::FileSourceFS customDataDir(".");
 
-int main(int argc, char **argv)
+extern "C" int main(int argc, char **argv)
 {
 #ifdef PIONEER_PROFILER
 	Profiler::detect(argc, argv);

src/savegamedump.cpp

@@ -4,8 +4,9 @@
 #include "FileSystem.h"
 #include "GZipFormat.h"
 #include "Json.h"
+#include <SDL.h>
 
-int main(int argc, const char **argv)
+extern "C" int main(int argc, char **argv)
 {
 	if (argc < 2 || argc > 3) {
 		printf(