Fixed bug #220

The AltiVec blitters don't compile, since they require __VEC__ to be enabled in
order for the compiler to understand "vector" and friends (i.e. do AltiVec)
But you don't want to turn AltiVec on globally, since then the code would only
run on a G4 (there are already runtime tests, before using the AltiVec
variants)

The solution here is to enable AltiVec locally, for the actual AltiVec code.

src/video/SDL_blit_A.c

@@ -637,6 +637,9 @@ static void BlitRGBtoRGBPixelAlphaMMX(SDL_BlitInfo *info)
 #endif /* GCC_ASMBLIT, MSVC_ASMBLIT */
 
 #if SDL_ALTIVEC_BLITTERS
+#if __MWERKS__
+#pragma altivec_model on
+#endif
 #if HAVE_ALTIVEC_H
 #include <altivec.h>
 #endif
@@ -1406,6 +1409,9 @@ static void BlitRGBtoRGBSurfaceAlphaAltivec(SDL_BlitInfo *info)
         dstp += dstskip;
     }
 }
+#if __MWERKS__
+#pragma altivec_model off
+#endif
 #endif /* SDL_ALTIVEC_BLITTERS */
 
 /* fast RGB888->(A)RGB888 blending with surface alpha=128 special case */

src/video/SDL_blit_N.c

@@ -29,6 +29,9 @@
 /* Functions to blit from N-bit surfaces to other surfaces */
 
 #if SDL_ALTIVEC_BLITTERS
+#if __MWERKS__
+#pragma altivec_model on
+#endif
 #ifdef HAVE_ALTIVEC_H
 #include <altivec.h>
 #endif
@@ -830,6 +833,9 @@ static Uint32 GetBlitFeatures( void )
     }
     return features;
 }
+#if __MWERKS__
+#pragma altivec_model off
+#endif
 #else
 /* Feature 1 is has-MMX */
 #define GetBlitFeatures() ((Uint32)(SDL_HasMMX() ? 1 : 0))