Allow the Altivec/VMX implementation on little-endian PowerPC. Together
with the vec_sld fix in easel/esl_vmx.h the vector code works on
powerpc64le too (same fix as biology/hmmer).

--- configure.orig	2023-09-06 14:14:14 UTC
+++ configure
@@ -7815,13 +7815,7 @@ printf "%s\n" "#define WORDS_BIGENDIAN 1" >>confdefs.h
   ;; #(
    no)

-  if test "$enable_vmx" = "yes"; then
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: ::::::::::--- no vector instruction set ---::::::::::" >&5
-printf "%s\n" "$as_me: ::::::::::--- no vector instruction set ---::::::::::" >&6;}
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: Infernal Altivec/VMX only supports big-endian platforms: e.g. ppc64 not ppc64le" >&5
-printf "%s\n" "$as_me: Infernal Altivec/VMX only supports big-endian platforms: e.g. ppc64 not ppc64le" >&6;}
-    as_fn_error $? "No supported vectorization found for your machine." "$LINENO" 5
-  elif test "$enable_neon" = "yes"; then
+  if test "$enable_neon" = "yes"; then
     as_CACHEVAR=`printf "%s\n" "ax_cv_check_cflags_$NEON_CFLAGS_-mlittle-endian" | $as_tr_sh`
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -mlittle-endian" >&5
 printf %s "checking whether C compiler accepts -mlittle-endian... " >&6; }
