move MSVC warning config

moved from `Pragma.h` to `CMakeLists.txt`

also updated justifications since some of them were out of date, incorrect, or unnecessarily editorial

CMakeLists.txt

@@ -88,11 +88,26 @@ if(MSVC)
     # see https://msdn.microsoft.com/en-us/library/074af4b6.aspx
     add_compile_options("/wd4503")
 
-    # suppress C4267 - VC++ complains whenever we implicitly convert an integer to
-    # a smaller type, and most of the time this is just conversion from 64 to 32 bits
-    # for things like vector sizes, which are never that big anyway.
+    # suppress C4267 - VC++ considers a narrowing conversion from size_t to a smaller
+    # integer type a warning. this is technically correct but there are so many instances
+    # of this that we don't want to fix, so....
     add_compile_options("/wd4267")
 
+    # suppress C4251 - VC++ will warn when exporting an entire class which contains members
+    # referencing unexported compound types is unsafe. because we don't guarantee a stable API
+    # for our exports, we don't really care about this, so we choose to be lazy and continue to
+    # export entire classes instead of exporting on a method-by-method basis
+    add_compile_options("/wd4251")
+
+    # suppress C4068 - VC++ will warn for unknown pragmas by default. this is equivalent to gcc
+    # -Wno-unknown-pragmas. we could work around this with sufficiently complex macros
+    add_compile_options("/wd4068")
+
+    # suppress C4244 - VC++ warns by default (with /Wall) about narrowing conversions that may lose data
+    # (such as double -> int or int32_t -> int16_t). dfhack has many of these, mostly related to Lua
+    # this is equivalent to gcc -Wno_conversions which is the default as gcc -Wall doesn't enable -Wconversions
+    add_compile_options("/wd4244")
+
     # MSVC panics if an object file contains more than 65,279 sections. this
     # happens quite frequently with code that uses templates, such as vectors.
     add_compile_options("/bigobj")

library/include/Pragma.h

@@ -28,14 +28,6 @@ distribution.
 #define DFHACK_TRANQUILITY
 
 #ifdef _MSC_VER
-    // don't generate warnings because we're lazy about how we do exports
-    #pragma warning( disable: 4251 )
-    // do not issue warning for unknown pragmas (equivalent to gcc -Wno-unknown-pragmas)
-    #pragma warning( disable: 4068 )
-    // disable warnings regarding narrowing conversions (equivalent to gcc -Wno-conversion)
-    #pragma warning( disable: 4244)
-    // disable warnings regarding narrowing conversions of size_t
-    #pragma warning( disable: 4267)
 #endif
 
 #endif