Fix link errors with older MinGW due to use of GetLayout()

This function is not present in older MinGW import libraries, up to at least
MinGW 4.8.1, so we can't use it directly as it was done in
22f0801378 and we need to load it dynamically.

This was already done in wxDC code, so just reuse the same wrapper function
after extracting it (and a few others, for consistency) into a new header.

src/msw/dc.cpp

@@ -240,13 +240,6 @@ wxIMPLEMENT_DYNAMIC_CLASS(wxGDIDLLsCleanupModule, wxModule);
 
 #endif // USE_DYNAMIC_GDI_FUNCS
 
-// Namespace for the wrapper functions, hopefully one day we'll be able to get
-// rid of all of them and then it will be easy to find all occurrences of their
-// use by just searching for this namespace name.
-//
-// All of the functions in this namespace must work *exactly* like the standard
-// functions with the same name and just return an error if dynamically loading
-// them failed.
 namespace wxDynLoadWrappers
 {
 
@@ -317,19 +310,16 @@ BOOL GradientFill(HDC hdc, PTRIVERTEX pVert, ULONG numVert,
 
 #elif defined(USE_STATIC_GDI_FUNCS)
 
-inline
 DWORD GetLayout(HDC hdc)
 {
     return ::GetLayout(hdc);
 }
 
-inline
 DWORD SetLayout(HDC hdc, DWORD dwLayout)
 {
     return ::SetLayout(hdc, dwLayout);
 }
 
-inline
 BOOL AlphaBlend(HDC hdcDest, int xDest, int yDest, int wDest, int hDest,
                 HDC hdcSrc, int xSrc, int ySrc, int wSrc, int hSrc,
                 BLENDFUNCTION bf)
@@ -339,7 +329,6 @@ BOOL AlphaBlend(HDC hdcDest, int xDest, int yDest, int wDest, int hDest,
                         bf);
 }
 
-inline
 BOOL GradientFill(HDC hdc, PTRIVERTEX pVert, ULONG numVert,
                   PVOID pMesh, ULONG numMesh, ULONG mode)
 {