postproc: altivec: fix trivial cases of mixed declarations and code

This moves declarations without initialisers or with constant
initialisers to the start of a block, and adds do {} while(0)
around some macros, thus allowing declarations within them.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libpostproc/postprocess_template.c

@@ -3518,9 +3518,10 @@ static void RENAME(postProcess)(const uint8_t src[], int srcStride, uint8_t dst[
                 else if(mode & H_DEBLOCK){
 #if HAVE_ALTIVEC
                     DECLARE_ALIGNED(16, unsigned char, tempBlock)[272];
+                    int t;
                     transpose_16x8_char_toPackedAlign_altivec(tempBlock, dstBlock - (4 + 1), stride);
 
-                    const int t=vertClassify_altivec(tempBlock-48, 16, &c);
+                    t = vertClassify_altivec(tempBlock-48, 16, &c);
                     if(t==1) {
                         doVertLowPass_altivec(tempBlock-48, 16, &c);
                         transpose_8x16_char_fromPackedAlign_altivec(dstBlock - (4 + 1), tempBlock, stride);