build: Turn on "treat warnings as errors" on Win

Also address compiler warnings:

- Suppress warnings for inconsistently redefined snprintf
  on Windows with Visual Studio < 2015.  Warnings for
  preprocessor redefinitions are still enabled on VS 2015
  because snprintf is not redefined on VS 2015.

- Turn off "changed behavior" warning with Visual Studio < 2015
  for using initializers in constructors.  MSFT "fixed" some
  forms of these initializers so that they clear members instead
  of just leaving them alone.  Since clearing is usually desired,
  this isn't a problem in most cases.  But if an object is
  reinstantiated on top of an existing object, via placement new
  for example, the clearing may not be desired if the first object's
  data was meant to be preserved.  We don't count on this behavior.

- Suppress linker warning for linking the loader in debug build on
  Windows.  This warning is for mismatched runtime libraries and
  causes extra code to be linked in only for debug builds.  Ignoring
  the warning is generally regarded as better than the alternatives.

Change-Id: I8b0e311d3c80a8dd9ac0cc95f764ed1123efa86f

CMakeLists.txt

@@ -57,8 +57,9 @@ if (CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
 endif()
 
 if(WIN32)
-    # Disable RTTI
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /GR-")
+    # Disable RTTI, Treat warnings as errors
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /GR- /WX")
 endif()
 
 if(NOT WIN32)

loader/CMakeLists.txt

@@ -90,6 +90,8 @@ if (WIN32)
     target_compile_options(loader-opt PUBLIC "$<$<CONFIG:DEBUG>:${LOCAL_C_FLAGS_REL}>")
     add_library(${API_LOWERCASE}-${MAJOR} SHARED $<TARGET_OBJECTS:loader-opt> $<TARGET_OBJECTS:loader-norm> ${CMAKE_CURRENT_BINARY_DIR}/${API_LOWERCASE}-${MAJOR}.def ${CMAKE_CURRENT_SOURCE_DIR}/loader.rc)
     add_library(VKstatic.${MAJOR} STATIC $<TARGET_OBJECTS:loader-opt> $<TARGET_OBJECTS:loader-norm>)
+    # Suppress conflicting libs warning for debug builds.
+    set_target_properties(${API_LOWERCASE}-${MAJOR} PROPERTIES LINK_FLAGS_DEBUG /ignore:4098)
     set_target_properties(VKstatic.${MAJOR} PROPERTIES OUTPUT_NAME VKstatic.${MAJOR})
     target_link_libraries(${API_LOWERCASE}-${MAJOR} shlwapi)
     target_link_libraries(VKstatic.${MAJOR} shlwapi)