Building igl statically and moving to the dep scripts

Fixing dep build script on Windows and removing some warnings.

Use bundled igl by default.

Not building with the dependency scripts if not explicitly stated. This way, it will stay in
Fix the libigl patch to include C source files in header only mode.

src/libigl/CMakeLists.txt

@@ -0,0 +1,14 @@
+project(libigl)
+cmake_minimum_required(VERSION 3.0)
+
+add_library(libigl INTERFACE)
+
+find_package(libigl QUIET)
+
+if(libigl_FOUND)
+    message(STATUS "IGL found, using system version...")
+    target_link_libraries(libigl INTERFACE igl::core)
+else()
+    message(STATUS "IGL NOT found, using bundled version...")
+    target_include_directories(libigl INTERFACE SYSTEM ${LIBDIR}/libigl)
+endif()