appveyor, CMake: Remove -flto; Resume mingw static

This is probably the cause of Crypto++ segfault (?)

appveyor.yml

@@ -9,7 +9,7 @@ environment:
   # Tell msys2 to inherit the current directory when starting the shell
   CHERE_INVOKING: 1
   matrix:
-    # - BUILD_TYPE: mingw
+    - BUILD_TYPE: mingw
     - BUILD_TYPE: msvc
 
 platform:

src/CMakeLists.txt

@@ -106,9 +106,9 @@ else()
         endif()
     endif()
 
-    if (NOT DEBUG)
-        add_compile_options("-flto")
-    endif()
+    # if (NOT DEBUG)
+    #    add_compile_options("-flto")
+    # endif()
 endif()
 
 add_subdirectory(common)