Move utility functions trimfront/back to tccpp.c

These are used in `libtcc.c` now and cannot remain in `tccpe.c`

tccpe.c

@@ -1563,22 +1563,6 @@ quit:
     return ret;
 }
 
-/* ------------------------------------------------------------- */
-static char *trimfront(char *p)
-{
-    while (*p && (unsigned char)*p <= ' ')
-        ++p;
-    return p;
-}
-
-static char *trimback(char *a, char *e)
-{
-    while (e > a && (unsigned char)e[-1] <= ' ')
-        --e;
-    *e = 0;;
-    return a;
-}
-
 /* ------------------------------------------------------------- */
 static int pe_load_def(TCCState *s1, int fd)
 {